[PATCH v4 1/1] efi_loader: expose the device-tree file name
Forward and backward compatibility of Linux kernel device-trees is sometimes missing. One solution approach is to load a kernel specific device-tree. This can either be done via a U-Boot scripts (like the one generated by Debian package flash-kernel or by a boot loader like GRUB. The boot loader approach currently requires to know the device-tree name before first boot which makes it unusable for generic images.
Expose the device-tree file name as EFI variable FdtFile. This will allow bootloaders to load a kernel specific device-tree.
The variable will not be exposed on ACPI based systems or if the environment variable fdtfile is not defined.
Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com --- v4: Generalize the description of the content of $fdtfile. v3: Add documentation v2: Use a unique GUID to enable future U-Boot independent standardization. Do not try to add the variable on ACPI based systems. --- doc/develop/uefi/uefi.rst | 14 ++++++++++++++ include/efi_loader.h | 5 +++++ lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ 3 files changed, 49 insertions(+)
diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst index fb16ac743a..702c490831 100644 --- a/doc/develop/uefi/uefi.rst +++ b/doc/develop/uefi/uefi.rst @@ -916,6 +916,20 @@ So our final format of the FilePathList[] is::
Loaded image - end node (0xff) - VenMedia - initrd_1 - [end node (0x01) - initrd_n ...] - end node (0xff)
+EFI variable FdtFile +~~~~~~~~~~~~~~~~~~~~ + +Ideally U-Boot would always expose a device-tree that can be used for booting +any operating systems. Unfortunately operating systems like Linux sometimes +break forward and backward compatibility. In this case there is a need to load +an operating system version specific device-tree. + +U-Boot has an environment variable fdtfile identifying the device-tree file to +load. The content of this variable is exposed as EFI variable Fdtfile, vendor +GUID d45dde69-3bd6-40e0-90d5-6b606aa57730. It contains the device-tree path +name as a NUL terminated ASCII string. On many architectures the file name is +preceded by a vendor directory ('vendor-directory/board-name.dtb'). + Links -----
diff --git a/include/efi_loader.h b/include/efi_loader.h index e24410505f..146e7f1bce 100644 --- a/include/efi_loader.h +++ b/include/efi_loader.h @@ -152,6 +152,11 @@ static inline efi_status_t efi_launch_capsules(void) EFI_GUID(0x8108ac4e, 0x9f11, 0x4d59, \ 0x85, 0x0e, 0xe2, 0x1a, 0x52, 0x2c, 0x59, 0xb2)
+/* Vendor GUID for the FdtFile variable */ +#define VENDOR_FDTFILE_GUID \ + EFI_GUID(0xd45dde69, 0x3bd6, 0x40e0, \ + 0x90, 0xd5, 0x6b, 0x60, 0x6a, 0xa5, 0x77, 0x30) + /* Use internal device tree when starting UEFI application */ #define EFI_FDT_USE_INTERNAL NULL
diff --git a/lib/efi_loader/efi_setup.c b/lib/efi_loader/efi_setup.c index e6de685e87..71bcde645b 100644 --- a/lib/efi_loader/efi_setup.c +++ b/lib/efi_loader/efi_setup.c @@ -17,6 +17,8 @@
efi_status_t efi_obj_list_initialized = OBJ_LIST_NOT_INITIALIZED;
+efi_guid_t vendor_fdtfile_guid = VENDOR_FDTFILE_GUID; + /* * Allow unaligned memory access. * @@ -26,6 +28,27 @@ void __weak allow_unaligned(void) { }
+/** + * efi_init_fdtfile() - set EFI variable FdtFile + * + * Return: status code + */ +static efi_status_t efi_init_fdtfile(void) +{ + char *val; + + val = env_get("fdtfile"); + if (!val) + return EFI_SUCCESS; + + return efi_set_variable_int(u"FdtFile", + &vendor_fdtfile_guid, + EFI_VARIABLE_BOOTSERVICE_ACCESS | + EFI_VARIABLE_RUNTIME_ACCESS | + EFI_VARIABLE_READ_ONLY, + strlen(val) + 1, val, false); +} + /** * efi_init_platform_lang() - define supported languages * @@ -250,6 +273,13 @@ efi_status_t efi_init_obj_list(void) if (ret != EFI_SUCCESS) goto out;
+ /* Define EFI variable FdtFile */ + if (!CONFIG_IS_ENABLED(GENERATE_ACPI_TABLE)) { + ret = efi_init_fdtfile(); + if (ret != EFI_SUCCESS) + goto out; + } + /* Indicate supported features */ ret = efi_init_os_indications(); if (ret != EFI_SUCCESS)
Hi Heinrich,
On Mon, 23 Oct 2023 at 23:20, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote:
Forward and backward compatibility of Linux kernel device-trees is sometimes missing. One solution approach is to load a kernel specific device-tree. This can either be done via a U-Boot scripts (like the one generated by Debian package flash-kernel or by a boot loader like GRUB. The boot loader approach currently requires to know the device-tree name before first boot which makes it unusable for generic images.
Expose the device-tree file name as EFI variable FdtFile. This will allow bootloaders to load a kernel specific device-tree.
kernel-specific
The variable will not be exposed on ACPI based systems or if the environment variable fdtfile is not defined.
Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com
v4: Generalize the description of the content of $fdtfile. v3: Add documentation v2: Use a unique GUID to enable future U-Boot independent standardization. Do not try to add the variable on ACPI based systems.
doc/develop/uefi/uefi.rst | 14 ++++++++++++++ include/efi_loader.h | 5 +++++ lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ 3 files changed, 49 insertions(+)
diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst index fb16ac743a..702c490831 100644 --- a/doc/develop/uefi/uefi.rst +++ b/doc/develop/uefi/uefi.rst @@ -916,6 +916,20 @@ So our final format of the FilePathList[] is::
Loaded image - end node (0xff) - VenMedia - initrd_1 - [end node (0x01) - initrd_n ...] - end node (0xff)+EFI variable FdtFile +~~~~~~~~~~~~~~~~~~~~
+Ideally U-Boot would always expose a device-tree that can be used for booting +any operating systems. Unfortunately operating systems like Linux sometimes +break forward and backward compatibility. In this case there is a need to load +an operating system version specific device-tree.
This seems to be a strong statement. Given the effort that goes into the DT, changes are supposed to be backwards-compatible. Is this generally true, or is it just that we want an up-to-date DT for the kernel to enable new features?
+U-Boot has an environment variable fdtfile identifying the device-tree file to +load. The content of this variable is exposed as EFI variable Fdtfile, vendor +GUID d45dde69-3bd6-40e0-90d5-6b606aa57730. It contains the device-tree path +name as a NUL terminated ASCII string. On many architectures the file name is
NUL-terminated
+preceded by a vendor directory ('vendor-directory/board-name.dtb').
Links
diff --git a/include/efi_loader.h b/include/efi_loader.h index e24410505f..146e7f1bce 100644 --- a/include/efi_loader.h +++ b/include/efi_loader.h @@ -152,6 +152,11 @@ static inline efi_status_t efi_launch_capsules(void) EFI_GUID(0x8108ac4e, 0x9f11, 0x4d59, \ 0x85, 0x0e, 0xe2, 0x1a, 0x52, 0x2c, 0x59, 0xb2)
+/* Vendor GUID for the FdtFile variable */ +#define VENDOR_FDTFILE_GUID \
EFI_GUID(0xd45dde69, 0x3bd6, 0x40e0, \0x90, 0xd5, 0x6b, 0x60, 0x6a, 0xa5, 0x77, 0x30)/* Use internal device tree when starting UEFI application */ #define EFI_FDT_USE_INTERNAL NULL
diff --git a/lib/efi_loader/efi_setup.c b/lib/efi_loader/efi_setup.c index e6de685e87..71bcde645b 100644 --- a/lib/efi_loader/efi_setup.c +++ b/lib/efi_loader/efi_setup.c @@ -17,6 +17,8 @@
efi_status_t efi_obj_list_initialized = OBJ_LIST_NOT_INITIALIZED;
+efi_guid_t vendor_fdtfile_guid = VENDOR_FDTFILE_GUID;
/*
- Allow unaligned memory access.
@@ -26,6 +28,27 @@ void __weak allow_unaligned(void) { }
+/**
- efi_init_fdtfile() - set EFI variable FdtFile
- Return: status code
- */
+static efi_status_t efi_init_fdtfile(void) +{
char *val;val = env_get("fdtfile");if (!val)return EFI_SUCCESS;return efi_set_variable_int(u"FdtFile",&vendor_fdtfile_guid,EFI_VARIABLE_BOOTSERVICE_ACCESS |EFI_VARIABLE_RUNTIME_ACCESS |EFI_VARIABLE_READ_ONLY,strlen(val) + 1, val, false);+}
/**
- efi_init_platform_lang() - define supported languages
@@ -250,6 +273,13 @@ efi_status_t efi_init_obj_list(void) if (ret != EFI_SUCCESS) goto out;
/* Define EFI variable FdtFile */if (!CONFIG_IS_ENABLED(GENERATE_ACPI_TABLE)) {ret = efi_init_fdtfile();if (ret != EFI_SUCCESS)goto out;}/* Indicate supported features */ ret = efi_init_os_indications(); if (ret != EFI_SUCCESS)-- 2.40.1
Assuming my concerns above are figured out:
Reviewed-by: Simon Glass sjg@chromium.org
Regards, SImon
Hi Heinrich,
On Tue, 24 Oct 2023 at 18:02, Simon Glass sjg@google.com wrote:
Hi Heinrich,
On Mon, 23 Oct 2023 at 23:20, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote:
Forward and backward compatibility of Linux kernel device-trees is sometimes missing. One solution approach is to load a kernel specific device-tree. This can either be done via a U-Boot scripts (like the one generated by Debian package flash-kernel or by a boot loader like GRUB. The boot loader approach currently requires to know the device-tree name before first boot which makes it unusable for generic images.
Expose the device-tree file name as EFI variable FdtFile. This will allow bootloaders to load a kernel specific device-tree.
kernel-specific
The variable will not be exposed on ACPI based systems or if the environment variable fdtfile is not defined.
Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com
v4: Generalize the description of the content of $fdtfile. v3: Add documentation v2: Use a unique GUID to enable future U-Boot independent standardization. Do not try to add the variable on ACPI based systems.
doc/develop/uefi/uefi.rst | 14 ++++++++++++++ include/efi_loader.h | 5 +++++ lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ 3 files changed, 49 insertions(+)
diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst index fb16ac743a..702c490831 100644 --- a/doc/develop/uefi/uefi.rst +++ b/doc/develop/uefi/uefi.rst @@ -916,6 +916,20 @@ So our final format of the FilePathList[] is::
Loaded image - end node (0xff) - VenMedia - initrd_1 - [end node (0x01) - initrd_n ...] - end node (0xff)+EFI variable FdtFile +~~~~~~~~~~~~~~~~~~~~
+Ideally U-Boot would always expose a device-tree that can be used for booting +any operating systems. Unfortunately operating systems like Linux sometimes +break forward and backward compatibility. In this case there is a need to load +an operating system version specific device-tree.
This seems to be a strong statement. Given the effort that goes into the DT, changes are supposed to be backwards-compatible. Is this generally true, or is it just that we want an up-to-date DT for the kernel to enable new features?
Did you see this comment?
Regards, Simon
+U-Boot has an environment variable fdtfile identifying the device-tree file to +load. The content of this variable is exposed as EFI variable Fdtfile, vendor +GUID d45dde69-3bd6-40e0-90d5-6b606aa57730. It contains the device-tree path +name as a NUL terminated ASCII string. On many architectures the file name is
NUL-terminated
+preceded by a vendor directory ('vendor-directory/board-name.dtb').
Links
diff --git a/include/efi_loader.h b/include/efi_loader.h index e24410505f..146e7f1bce 100644 --- a/include/efi_loader.h +++ b/include/efi_loader.h @@ -152,6 +152,11 @@ static inline efi_status_t efi_launch_capsules(void) EFI_GUID(0x8108ac4e, 0x9f11, 0x4d59, \ 0x85, 0x0e, 0xe2, 0x1a, 0x52, 0x2c, 0x59, 0xb2)
+/* Vendor GUID for the FdtFile variable */ +#define VENDOR_FDTFILE_GUID \
EFI_GUID(0xd45dde69, 0x3bd6, 0x40e0, \0x90, 0xd5, 0x6b, 0x60, 0x6a, 0xa5, 0x77, 0x30)/* Use internal device tree when starting UEFI application */ #define EFI_FDT_USE_INTERNAL NULL
diff --git a/lib/efi_loader/efi_setup.c b/lib/efi_loader/efi_setup.c index e6de685e87..71bcde645b 100644 --- a/lib/efi_loader/efi_setup.c +++ b/lib/efi_loader/efi_setup.c @@ -17,6 +17,8 @@
efi_status_t efi_obj_list_initialized = OBJ_LIST_NOT_INITIALIZED;
+efi_guid_t vendor_fdtfile_guid = VENDOR_FDTFILE_GUID;
/*
- Allow unaligned memory access.
@@ -26,6 +28,27 @@ void __weak allow_unaligned(void) { }
+/**
- efi_init_fdtfile() - set EFI variable FdtFile
- Return: status code
- */
+static efi_status_t efi_init_fdtfile(void) +{
char *val;val = env_get("fdtfile");if (!val)return EFI_SUCCESS;return efi_set_variable_int(u"FdtFile",&vendor_fdtfile_guid,EFI_VARIABLE_BOOTSERVICE_ACCESS |EFI_VARIABLE_RUNTIME_ACCESS |EFI_VARIABLE_READ_ONLY,strlen(val) + 1, val, false);+}
/**
- efi_init_platform_lang() - define supported languages
@@ -250,6 +273,13 @@ efi_status_t efi_init_obj_list(void) if (ret != EFI_SUCCESS) goto out;
/* Define EFI variable FdtFile */if (!CONFIG_IS_ENABLED(GENERATE_ACPI_TABLE)) {ret = efi_init_fdtfile();if (ret != EFI_SUCCESS)goto out;}/* Indicate supported features */ ret = efi_init_os_indications(); if (ret != EFI_SUCCESS)-- 2.40.1
Assuming my concerns above are figured out:
Reviewed-by: Simon Glass sjg@chromium.org
Regards, SImon
On 10/25/23 20:23, Simon Glass wrote:
Hi Heinrich,
On Tue, 24 Oct 2023 at 18:02, Simon Glass sjg@google.com wrote:
Hi Heinrich,
On Mon, 23 Oct 2023 at 23:20, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote:
Forward and backward compatibility of Linux kernel device-trees is sometimes missing. One solution approach is to load a kernel specific device-tree. This can either be done via a U-Boot scripts (like the one generated by Debian package flash-kernel or by a boot loader like GRUB. The boot loader approach currently requires to know the device-tree name before first boot which makes it unusable for generic images.
Expose the device-tree file name as EFI variable FdtFile. This will allow bootloaders to load a kernel specific device-tree.
kernel-specific
The variable will not be exposed on ACPI based systems or if the environment variable fdtfile is not defined.
Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com
v4: Generalize the description of the content of $fdtfile. v3: Add documentation v2: Use a unique GUID to enable future U-Boot independent standardization. Do not try to add the variable on ACPI based systems.
doc/develop/uefi/uefi.rst | 14 ++++++++++++++ include/efi_loader.h | 5 +++++ lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ 3 files changed, 49 insertions(+)
diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst index fb16ac743a..702c490831 100644 --- a/doc/develop/uefi/uefi.rst +++ b/doc/develop/uefi/uefi.rst @@ -916,6 +916,20 @@ So our final format of the FilePathList[] is::
Loaded image - end node (0xff) - VenMedia - initrd_1 - [end node (0x01) - initrd_n ...] - end node (0xff)+EFI variable FdtFile +~~~~~~~~~~~~~~~~~~~~
+Ideally U-Boot would always expose a device-tree that can be used for booting +any operating systems. Unfortunately operating systems like Linux sometimes +break forward and backward compatibility. In this case there is a need to load +an operating system version specific device-tree.
This seems to be a strong statement. Given the effort that goes into the DT, changes are supposed to be backwards-compatible. Is this generally true, or is it just that we want an up-to-date DT for the kernel to enable new features?
Did you see this comment?
It would have been nice to put the person which made that comment on copy.
The truth lies in the world "supposed":
The idea of a device-tree that never needs to change is quite old and never became true on ARM devices.
We all know Linux tends to break both forward and backward compatibility of device-trees. Here is a nice example:
d0c6707ca423 ("arm64: dts: allwinner: H5: NanoPi Neo Plus2: phy-mode rgmii-id")
Driver changes broke forward and backwards compatibility of a lot of Allwinner boards.
Distros will continue to load the device-tree that matches the kernel to get the best possible board support and need to do this efficiently.
Best regards
Heinrich
Regards, Simon
+U-Boot has an environment variable fdtfile identifying the device-tree file to +load. The content of this variable is exposed as EFI variable Fdtfile, vendor +GUID d45dde69-3bd6-40e0-90d5-6b606aa57730. It contains the device-tree path +name as a NUL terminated ASCII string. On many architectures the file name is
NUL-terminated
+preceded by a vendor directory ('vendor-directory/board-name.dtb').
Links
diff --git a/include/efi_loader.h b/include/efi_loader.h index e24410505f..146e7f1bce 100644 --- a/include/efi_loader.h +++ b/include/efi_loader.h @@ -152,6 +152,11 @@ static inline efi_status_t efi_launch_capsules(void) EFI_GUID(0x8108ac4e, 0x9f11, 0x4d59, \ 0x85, 0x0e, 0xe2, 0x1a, 0x52, 0x2c, 0x59, 0xb2)
+/* Vendor GUID for the FdtFile variable */ +#define VENDOR_FDTFILE_GUID \
EFI_GUID(0xd45dde69, 0x3bd6, 0x40e0, \0x90, 0xd5, 0x6b, 0x60, 0x6a, 0xa5, 0x77, 0x30)- /* Use internal device tree when starting UEFI application */ #define EFI_FDT_USE_INTERNAL NULL
diff --git a/lib/efi_loader/efi_setup.c b/lib/efi_loader/efi_setup.c index e6de685e87..71bcde645b 100644 --- a/lib/efi_loader/efi_setup.c +++ b/lib/efi_loader/efi_setup.c @@ -17,6 +17,8 @@
efi_status_t efi_obj_list_initialized = OBJ_LIST_NOT_INITIALIZED;
+efi_guid_t vendor_fdtfile_guid = VENDOR_FDTFILE_GUID;
- /*
- Allow unaligned memory access.
@@ -26,6 +28,27 @@ void __weak allow_unaligned(void) { }
+/**
- efi_init_fdtfile() - set EFI variable FdtFile
- Return: status code
- */
+static efi_status_t efi_init_fdtfile(void) +{
char *val;val = env_get("fdtfile");if (!val)return EFI_SUCCESS;return efi_set_variable_int(u"FdtFile",&vendor_fdtfile_guid,EFI_VARIABLE_BOOTSERVICE_ACCESS |EFI_VARIABLE_RUNTIME_ACCESS |EFI_VARIABLE_READ_ONLY,strlen(val) + 1, val, false);+}
- /**
- efi_init_platform_lang() - define supported languages
@@ -250,6 +273,13 @@ efi_status_t efi_init_obj_list(void) if (ret != EFI_SUCCESS) goto out;
/* Define EFI variable FdtFile */if (!CONFIG_IS_ENABLED(GENERATE_ACPI_TABLE)) {ret = efi_init_fdtfile();if (ret != EFI_SUCCESS)goto out;}/* Indicate supported features */ ret = efi_init_os_indications(); if (ret != EFI_SUCCESS)-- 2.40.1
Assuming my concerns above are figured out:
Reviewed-by: Simon Glass sjg@chromium.org
Regards, SImon
On Wed, Oct 25, 2023 at 09:57:44PM +0200, Heinrich Schuchardt wrote:
On 10/25/23 20:23, Simon Glass wrote:
Hi Heinrich,
On Tue, 24 Oct 2023 at 18:02, Simon Glass sjg@google.com wrote:
Hi Heinrich,
On Mon, 23 Oct 2023 at 23:20, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote:
Forward and backward compatibility of Linux kernel device-trees is sometimes missing. One solution approach is to load a kernel specific device-tree. This can either be done via a U-Boot scripts (like the one generated by Debian package flash-kernel or by a boot loader like GRUB. The boot loader approach currently requires to know the device-tree name before first boot which makes it unusable for generic images.
Expose the device-tree file name as EFI variable FdtFile. This will allow bootloaders to load a kernel specific device-tree.
kernel-specific
The variable will not be exposed on ACPI based systems or if the environment variable fdtfile is not defined.
Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com
v4: Generalize the description of the content of $fdtfile. v3: Add documentation v2: Use a unique GUID to enable future U-Boot independent standardization. Do not try to add the variable on ACPI based systems.
doc/develop/uefi/uefi.rst | 14 ++++++++++++++ include/efi_loader.h | 5 +++++ lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ 3 files changed, 49 insertions(+)
diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst index fb16ac743a..702c490831 100644 --- a/doc/develop/uefi/uefi.rst +++ b/doc/develop/uefi/uefi.rst @@ -916,6 +916,20 @@ So our final format of the FilePathList[] is::
Loaded image - end node (0xff) - VenMedia - initrd_1 - [end node (0x01) - initrd_n ...] - end node (0xff)+EFI variable FdtFile +~~~~~~~~~~~~~~~~~~~~
+Ideally U-Boot would always expose a device-tree that can be used for booting +any operating systems. Unfortunately operating systems like Linux sometimes +break forward and backward compatibility. In this case there is a need to load +an operating system version specific device-tree.
This seems to be a strong statement. Given the effort that goes into the DT, changes are supposed to be backwards-compatible. Is this generally true, or is it just that we want an up-to-date DT for the kernel to enable new features?
Did you see this comment?
It would have been nice to put the person which made that comment on copy.
The truth lies in the world "supposed":
The idea of a device-tree that never needs to change is quite old and never became true on ARM devices.
We all know Linux tends to break both forward and backward compatibility of device-trees. Here is a nice example:
d0c6707ca423 ("arm64: dts: allwinner: H5: NanoPi Neo Plus2: phy-mode rgmii-id")
Driver changes broke forward and backwards compatibility of a lot of Allwinner boards.
Distros will continue to load the device-tree that matches the kernel to get the best possible board support and need to do this efficiently.
Right, OK. And I think we want to try and have things phrased in a more neutral and less confrontational manner is part of the issue. Maybe:
In ideal circumstances, U-Boot will be able to expose the device-tree it is using to boot any operation system. However, in some cases operating systems need to load a specific device-tree rather than utilize the same one that U-Boot is currently using. In this case there is a need to load a specific device-tree binary from another location.
And as a more general concern I see right now, "fdt_file" and "fdtfile" are both used today, including new rather than older platforms that might avoid EFI_LOADER all the same, perhaps we should check for both? Or do you instead want to get board maintainers to switch over, as fdt_file isn't listed under doc/ today.
Date: Wed, 25 Oct 2023 21:57:44 +0200 From: Heinrich Schuchardt heinrich.schuchardt@canonical.com
On 10/25/23 20:23, Simon Glass wrote:
Hi Heinrich,
On Tue, 24 Oct 2023 at 18:02, Simon Glass sjg@google.com wrote:
Hi Heinrich,
On Mon, 23 Oct 2023 at 23:20, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote:
Forward and backward compatibility of Linux kernel device-trees is sometimes missing. One solution approach is to load a kernel specific device-tree. This can either be done via a U-Boot scripts (like the one generated by Debian package flash-kernel or by a boot loader like GRUB. The boot loader approach currently requires to know the device-tree name before first boot which makes it unusable for generic images.
Expose the device-tree file name as EFI variable FdtFile. This will allow bootloaders to load a kernel specific device-tree.
kernel-specific
The variable will not be exposed on ACPI based systems or if the environment variable fdtfile is not defined.
Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com
v4: Generalize the description of the content of $fdtfile. v3: Add documentation v2: Use a unique GUID to enable future U-Boot independent standardization. Do not try to add the variable on ACPI based systems.
doc/develop/uefi/uefi.rst | 14 ++++++++++++++ include/efi_loader.h | 5 +++++ lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ 3 files changed, 49 insertions(+)
diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst index fb16ac743a..702c490831 100644 --- a/doc/develop/uefi/uefi.rst +++ b/doc/develop/uefi/uefi.rst @@ -916,6 +916,20 @@ So our final format of the FilePathList[] is::
Loaded image - end node (0xff) - VenMedia - initrd_1 - [end node (0x01) - initrd_n ...] - end node (0xff)+EFI variable FdtFile +~~~~~~~~~~~~~~~~~~~~
+Ideally U-Boot would always expose a device-tree that can be used for booting +any operating systems. Unfortunately operating systems like Linux sometimes +break forward and backward compatibility. In this case there is a need to load +an operating system version specific device-tree.
This seems to be a strong statement. Given the effort that goes into the DT, changes are supposed to be backwards-compatible. Is this generally true, or is it just that we want an up-to-date DT for the kernel to enable new features?
Did you see this comment?
It would have been nice to put the person which made that comment on copy.
The truth lies in the world "supposed":
The idea of a device-tree that never needs to change is quite old and never became true on ARM devices.
We all know Linux tends to break both forward and backward compatibility of device-trees. Here is a nice example:
d0c6707ca423 ("arm64: dts: allwinner: H5: NanoPi Neo Plus2: phy-mode rgmii-id")
Driver changes broke forward and backwards compatibility of a lot of Allwinner boards.
Well, that happened in 2020. Things have gotten better over time.
Distros will continue to load the device-tree that matches the kernel to get the best possible board support and need to do this efficiently.
Right. Even if there is full backward/forward compatibility, you probably want the latest device-tree to make sure you get the most complete hardware support.
But this shouldn't be used as an argument to not care about backward/forward compatibility.
On 10/25/23 22:28, Mark Kettenis wrote:
Date: Wed, 25 Oct 2023 21:57:44 +0200 From: Heinrich Schuchardt heinrich.schuchardt@canonical.com
On 10/25/23 20:23, Simon Glass wrote:
Hi Heinrich,
On Tue, 24 Oct 2023 at 18:02, Simon Glass sjg@google.com wrote:
Hi Heinrich,
On Mon, 23 Oct 2023 at 23:20, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote:
Forward and backward compatibility of Linux kernel device-trees is sometimes missing. One solution approach is to load a kernel specific device-tree. This can either be done via a U-Boot scripts (like the one generated by Debian package flash-kernel or by a boot loader like GRUB. The boot loader approach currently requires to know the device-tree name before first boot which makes it unusable for generic images.
Expose the device-tree file name as EFI variable FdtFile. This will allow bootloaders to load a kernel specific device-tree.
kernel-specific
The variable will not be exposed on ACPI based systems or if the environment variable fdtfile is not defined.
Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com
v4: Generalize the description of the content of $fdtfile. v3: Add documentation v2: Use a unique GUID to enable future U-Boot independent standardization. Do not try to add the variable on ACPI based systems.
doc/develop/uefi/uefi.rst | 14 ++++++++++++++ include/efi_loader.h | 5 +++++ lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ 3 files changed, 49 insertions(+)
diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst index fb16ac743a..702c490831 100644 --- a/doc/develop/uefi/uefi.rst +++ b/doc/develop/uefi/uefi.rst @@ -916,6 +916,20 @@ So our final format of the FilePathList[] is::
Loaded image - end node (0xff) - VenMedia - initrd_1 - [end node (0x01) - initrd_n ...] - end node (0xff)+EFI variable FdtFile +~~~~~~~~~~~~~~~~~~~~
+Ideally U-Boot would always expose a device-tree that can be used for booting +any operating systems. Unfortunately operating systems like Linux sometimes +break forward and backward compatibility. In this case there is a need to load +an operating system version specific device-tree.
This seems to be a strong statement. Given the effort that goes into the DT, changes are supposed to be backwards-compatible. Is this generally true, or is it just that we want an up-to-date DT for the kernel to enable new features?
Did you see this comment?
It would have been nice to put the person which made that comment on copy.
The truth lies in the world "supposed":
The idea of a device-tree that never needs to change is quite old and never became true on ARM devices.
We all know Linux tends to break both forward and backward compatibility of device-trees. Here is a nice example:
d0c6707ca423 ("arm64: dts: allwinner: H5: NanoPi Neo Plus2: phy-mode rgmii-id")
Driver changes broke forward and backwards compatibility of a lot of Allwinner boards.
Well, that happened in 2020. Things have gotten better over time.
The 2020 event struck me because a Linux kernel would not even be compatible with the device-tree of the same kernel release.
This year I once again had issues with booting an Allwinner board with a device-tree from a different Debian kernel version. Both backward and forward compatibility were broken. But at least I could boot with a matching device-tree.
Distros will continue to load the device-tree that matches the kernel to get the best possible board support and need to do this efficiently.
Right. Even if there is full backward/forward compatibility, you probably want the latest device-tree to make sure you get the most complete hardware support.
But this shouldn't be used as an argument to not care about backward/forward compatibility.
Nobody in this thread suggested to not care about forward and backward compatibility.
Best regards
Heinrich
Hi Heinrich,
On Wed, 25 Oct 2023 at 20:51, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote:
On 10/25/23 22:28, Mark Kettenis wrote:
Date: Wed, 25 Oct 2023 21:57:44 +0200 From: Heinrich Schuchardt heinrich.schuchardt@canonical.com
On 10/25/23 20:23, Simon Glass wrote:
Hi Heinrich,
On Tue, 24 Oct 2023 at 18:02, Simon Glass sjg@google.com wrote:
Hi Heinrich,
On Mon, 23 Oct 2023 at 23:20, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote:
Forward and backward compatibility of Linux kernel device-trees is sometimes missing. One solution approach is to load a kernel specific device-tree. This can either be done via a U-Boot scripts (like the one generated by Debian package flash-kernel or by a boot loader like GRUB. The boot loader approach currently requires to know the device-tree name before first boot which makes it unusable for generic images.
Expose the device-tree file name as EFI variable FdtFile. This will allow bootloaders to load a kernel specific device-tree.
kernel-specific
The variable will not be exposed on ACPI based systems or if the environment variable fdtfile is not defined.
Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com
v4: Generalize the description of the content of $fdtfile. v3: Add documentation v2: Use a unique GUID to enable future U-Boot independent standardization. Do not try to add the variable on ACPI based systems.
doc/develop/uefi/uefi.rst | 14 ++++++++++++++ include/efi_loader.h | 5 +++++ lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ 3 files changed, 49 insertions(+)
diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst index fb16ac743a..702c490831 100644 --- a/doc/develop/uefi/uefi.rst +++ b/doc/develop/uefi/uefi.rst @@ -916,6 +916,20 @@ So our final format of the FilePathList[] is::
Loaded image - end node (0xff) - VenMedia - initrd_1 - [end node (0x01) - initrd_n ...] - end node (0xff)+EFI variable FdtFile +~~~~~~~~~~~~~~~~~~~~
+Ideally U-Boot would always expose a device-tree that can be used for booting +any operating systems. Unfortunately operating systems like Linux sometimes +break forward and backward compatibility. In this case there is a need to load +an operating system version specific device-tree.
This seems to be a strong statement. Given the effort that goes into the DT, changes are supposed to be backwards-compatible. Is this generally true, or is it just that we want an up-to-date DT for the kernel to enable new features?
Did you see this comment?
It would have been nice to put the person which made that comment on copy.
The truth lies in the world "supposed":
The idea of a device-tree that never needs to change is quite old and never became true on ARM devices.
We all know Linux tends to break both forward and backward compatibility of device-trees. Here is a nice example:
d0c6707ca423 ("arm64: dts: allwinner: H5: NanoPi Neo Plus2: phy-mode rgmii-id")
Driver changes broke forward and backwards compatibility of a lot of Allwinner boards.
Well, that happened in 2020. Things have gotten better over time.
The 2020 event struck me because a Linux kernel would not even be compatible with the device-tree of the same kernel release.
This year I once again had issues with booting an Allwinner board with a device-tree from a different Debian kernel version. Both backward and forward compatibility were broken. But at least I could boot with a matching device-tree.
Oh dear.
Distros will continue to load the device-tree that matches the kernel to get the best possible board support and need to do this efficiently.
Right. Even if there is full backward/forward compatibility, you probably want the latest device-tree to make sure you get the most complete hardware support.
But this shouldn't be used as an argument to not care about backward/forward compatibility.
Nobody in this thread suggested to not care about forward and backward compatibility.
The key thing we need to agree on is that the compatible string is the source of truth for booting. You check the model compatible and search for a matching DT with the best match, taking into account board revisions, etc. It is defined to be correct. If for some reason this process is wrong, then the board *should not boot*.
So anything which suggests that the above is not correct, or doesn't always work, or doesn't work well with EFI...is really going in the wrong direction.
Of course there will be workarounds, like this one, but the 'correct' way of doing it must still work. Nor is it 'slow' to do this, as I have demonstrated.
Perhaps we should add a compatible check into U-Boot, to make sure we are not choosing the wrong DT? At least for me, trying to get the filename right is a bit of a pain, with so many characters looking the same.
Regards, Simon
On Wed, Oct 25, 2023 at 10:28:05PM +0200, Mark Kettenis wrote:
Date: Wed, 25 Oct 2023 21:57:44 +0200 From: Heinrich Schuchardt heinrich.schuchardt@canonical.com
On 10/25/23 20:23, Simon Glass wrote:
Hi Heinrich,
On Tue, 24 Oct 2023 at 18:02, Simon Glass sjg@google.com wrote:
Hi Heinrich,
On Mon, 23 Oct 2023 at 23:20, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote:
Forward and backward compatibility of Linux kernel device-trees is sometimes missing. One solution approach is to load a kernel specific device-tree. This can either be done via a U-Boot scripts (like the one generated by Debian package flash-kernel or by a boot loader like GRUB. The boot loader approach currently requires to know the device-tree name before first boot which makes it unusable for generic images.
Expose the device-tree file name as EFI variable FdtFile. This will allow bootloaders to load a kernel specific device-tree.
kernel-specific
The variable will not be exposed on ACPI based systems or if the environment variable fdtfile is not defined.
Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com
v4: Generalize the description of the content of $fdtfile. v3: Add documentation v2: Use a unique GUID to enable future U-Boot independent standardization. Do not try to add the variable on ACPI based systems.
doc/develop/uefi/uefi.rst | 14 ++++++++++++++ include/efi_loader.h | 5 +++++ lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ 3 files changed, 49 insertions(+)
diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst index fb16ac743a..702c490831 100644 --- a/doc/develop/uefi/uefi.rst +++ b/doc/develop/uefi/uefi.rst @@ -916,6 +916,20 @@ So our final format of the FilePathList[] is::
Loaded image - end node (0xff) - VenMedia - initrd_1 - [end node (0x01) - initrd_n ...] - end node (0xff)+EFI variable FdtFile +~~~~~~~~~~~~~~~~~~~~
+Ideally U-Boot would always expose a device-tree that can be used for booting +any operating systems. Unfortunately operating systems like Linux sometimes +break forward and backward compatibility. In this case there is a need to load +an operating system version specific device-tree.
This seems to be a strong statement. Given the effort that goes into the DT, changes are supposed to be backwards-compatible. Is this generally true, or is it just that we want an up-to-date DT for the kernel to enable new features?
Did you see this comment?
It would have been nice to put the person which made that comment on copy.
The truth lies in the world "supposed":
The idea of a device-tree that never needs to change is quite old and never became true on ARM devices.
We all know Linux tends to break both forward and backward compatibility of device-trees. Here is a nice example:
d0c6707ca423 ("arm64: dts: allwinner: H5: NanoPi Neo Plus2: phy-mode rgmii-id")
Driver changes broke forward and backwards compatibility of a lot of Allwinner boards.
Well, that happened in 2020. Things have gotten better over time.
Well, yes and no. Given the brief summary here, I bet this was just like when phy-mode and am335x platforms had DT compatibility broken and the answer was that it was OK because the DT was incorrectly describing hardware. So this is the reminder that there are cases of breaking DT compatibility that are allowed. Even if the DT has been out (and wrong) for several years.
That's not the main point of this thread and I don't want to derail things further along this point, I just want to note that the details here reminded me of when things are allowed to be incompatible with previous trees.
On 10/25/23 23:13, Tom Rini wrote:
On Wed, Oct 25, 2023 at 10:28:05PM +0200, Mark Kettenis wrote:
Date: Wed, 25 Oct 2023 21:57:44 +0200 From: Heinrich Schuchardt heinrich.schuchardt@canonical.com
On 10/25/23 20:23, Simon Glass wrote:
Hi Heinrich,
On Tue, 24 Oct 2023 at 18:02, Simon Glass sjg@google.com wrote:
Hi Heinrich,
On Mon, 23 Oct 2023 at 23:20, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote:
Forward and backward compatibility of Linux kernel device-trees is sometimes missing. One solution approach is to load a kernel specific device-tree. This can either be done via a U-Boot scripts (like the one generated by Debian package flash-kernel or by a boot loader like GRUB. The boot loader approach currently requires to know the device-tree name before first boot which makes it unusable for generic images.
Expose the device-tree file name as EFI variable FdtFile. This will allow bootloaders to load a kernel specific device-tree.
kernel-specific
The variable will not be exposed on ACPI based systems or if the environment variable fdtfile is not defined.
Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com
v4: Generalize the description of the content of $fdtfile. v3: Add documentation v2: Use a unique GUID to enable future U-Boot independent standardization. Do not try to add the variable on ACPI based systems.
doc/develop/uefi/uefi.rst | 14 ++++++++++++++ include/efi_loader.h | 5 +++++ lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ 3 files changed, 49 insertions(+)
diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst index fb16ac743a..702c490831 100644 --- a/doc/develop/uefi/uefi.rst +++ b/doc/develop/uefi/uefi.rst @@ -916,6 +916,20 @@ So our final format of the FilePathList[] is::
Loaded image - end node (0xff) - VenMedia - initrd_1 - [end node (0x01) - initrd_n ...] - end node (0xff)+EFI variable FdtFile +~~~~~~~~~~~~~~~~~~~~
+Ideally U-Boot would always expose a device-tree that can be used for booting +any operating systems. Unfortunately operating systems like Linux sometimes +break forward and backward compatibility. In this case there is a need to load +an operating system version specific device-tree.
This seems to be a strong statement. Given the effort that goes into the DT, changes are supposed to be backwards-compatible. Is this generally true, or is it just that we want an up-to-date DT for the kernel to enable new features?
Did you see this comment?
It would have been nice to put the person which made that comment on copy.
The truth lies in the world "supposed":
The idea of a device-tree that never needs to change is quite old and never became true on ARM devices.
We all know Linux tends to break both forward and backward compatibility of device-trees. Here is a nice example:
d0c6707ca423 ("arm64: dts: allwinner: H5: NanoPi Neo Plus2: phy-mode rgmii-id")
Driver changes broke forward and backwards compatibility of a lot of Allwinner boards.
Well, that happened in 2020. Things have gotten better over time.
Well, yes and no. Given the brief summary here, I bet this was just like when phy-mode and am335x platforms had DT compatibility broken and the answer was that it was OK because the DT was incorrectly describing hardware. So this is the reminder that there are cases of breaking DT compatibility that are allowed. Even if the DT has been out (and wrong) for several years.
That's not the main point of this thread and I don't want to derail things further along this point, I just want to note that the details here reminded me of when things are allowed to be incompatible with previous trees.
You are conflating things:
The EFI variable is a hint to the GRUB OS to find the correct device-tree file without scanning hundreds of device-tree. You can not build a compatibility check for it into U-Boot.
In distro-boot we are using the same value from environment variable $fdtfile. Here you could check the compatible string but this might break booting .
Best regards
Heinrich
Hi Heinrich,
On Wed, 25 Oct 2023 at 15:22, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote:
On 10/25/23 23:13, Tom Rini wrote:
On Wed, Oct 25, 2023 at 10:28:05PM +0200, Mark Kettenis wrote:
Date: Wed, 25 Oct 2023 21:57:44 +0200 From: Heinrich Schuchardt heinrich.schuchardt@canonical.com
On 10/25/23 20:23, Simon Glass wrote:
Hi Heinrich,
On Tue, 24 Oct 2023 at 18:02, Simon Glass sjg@google.com wrote:
Hi Heinrich,
On Mon, 23 Oct 2023 at 23:20, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote: > > Forward and backward compatibility of Linux kernel device-trees is > sometimes missing. One solution approach is to load a kernel specific > device-tree. This can either be done via a U-Boot scripts (like the one > generated by Debian package flash-kernel or by a boot loader like GRUB. > The boot loader approach currently requires to know the device-tree name > before first boot which makes it unusable for generic images. > > Expose the device-tree file name as EFI variable FdtFile. > This will allow bootloaders to load a kernel specific device-tree.
kernel-specific
> > The variable will not be exposed on ACPI based systems or if the > environment variable fdtfile is not defined. > > Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com > --- > v4: > Generalize the description of the content of $fdtfile. > v3: > Add documentation > v2: > Use a unique GUID to enable future U-Boot independent > standardization. > Do not try to add the variable on ACPI based systems. > --- > doc/develop/uefi/uefi.rst | 14 ++++++++++++++ > include/efi_loader.h | 5 +++++ > lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ > 3 files changed, 49 insertions(+) > > diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst > index fb16ac743a..702c490831 100644 > --- a/doc/develop/uefi/uefi.rst > +++ b/doc/develop/uefi/uefi.rst > @@ -916,6 +916,20 @@ So our final format of the FilePathList[] is:: > > Loaded image - end node (0xff) - VenMedia - initrd_1 - [end node (0x01) - initrd_n ...] - end node (0xff) > > +EFI variable FdtFile > +~~~~~~~~~~~~~~~~~~~~ > + > +Ideally U-Boot would always expose a device-tree that can be used for booting > +any operating systems. Unfortunately operating systems like Linux sometimes > +break forward and backward compatibility. In this case there is a need to load > +an operating system version specific device-tree.
This seems to be a strong statement. Given the effort that goes into the DT, changes are supposed to be backwards-compatible. Is this generally true, or is it just that we want an up-to-date DT for the kernel to enable new features?
Did you see this comment?
It would have been nice to put the person which made that comment on copy.
The truth lies in the world "supposed":
The idea of a device-tree that never needs to change is quite old and never became true on ARM devices.
We all know Linux tends to break both forward and backward compatibility of device-trees. Here is a nice example:
d0c6707ca423 ("arm64: dts: allwinner: H5: NanoPi Neo Plus2: phy-mode rgmii-id")
Driver changes broke forward and backwards compatibility of a lot of Allwinner boards.
Well, that happened in 2020. Things have gotten better over time.
Well, yes and no. Given the brief summary here, I bet this was just like when phy-mode and am335x platforms had DT compatibility broken and the answer was that it was OK because the DT was incorrectly describing hardware. So this is the reminder that there are cases of breaking DT compatibility that are allowed. Even if the DT has been out (and wrong) for several years.
That's not the main point of this thread and I don't want to derail things further along this point, I just want to note that the details here reminded me of when things are allowed to be incompatible with previous trees.
Unfortunately I was off the list for a week or so, but I see this one so will reply here.
You are conflating things:
The EFI variable is a hint to the GRUB OS to find the correct device-tree file without scanning hundreds of device-tree. You can not build a compatibility check for it into U-Boot.
Actually we can...and I think that is what we should do.
In distro-boot we are using the same value from environment variable $fdtfile. Here you could check the compatible string but this might break booting .
We need to figure that point out. The compatible string is programmatically is defined to be correct, so it is the filename that may/may not be useful. What am I missing?
For distro-boot, do you mean the scripts? We are trying to deprecate those. Of course we have brought in all the same work-arounds, etc., but with bootstd we can start to clean things up, I hope.
So let's think about how we can have U-Boot choose the right DT to boot with.
Regards, Simon
On Tue, Oct 24, 2023 at 08:20:32AM +0200, Heinrich Schuchardt wrote:
Forward and backward compatibility of Linux kernel device-trees is sometimes missing. One solution approach is to load a kernel specific device-tree. This can either be done via a U-Boot scripts (like the one generated by Debian package flash-kernel or by a boot loader like GRUB. The boot loader approach currently requires to know the device-tree name before first boot which makes it unusable for generic images.
Expose the device-tree file name as EFI variable FdtFile. This will allow bootloaders to load a kernel specific device-tree.
The variable will not be exposed on ACPI based systems or if the environment variable fdtfile is not defined.
Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com
Reviewed-by: Tom Rini trini@konsulko.com
On Tue, 24 Oct 2023 at 09:20, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote:
Forward and backward compatibility of Linux kernel device-trees is sometimes missing. One solution approach is to load a kernel specific device-tree. This can either be done via a U-Boot scripts (like the one generated by Debian package flash-kernel or by a boot loader like GRUB. The boot loader approach currently requires to know the device-tree name before first boot which makes it unusable for generic images.
Expose the device-tree file name as EFI variable FdtFile. This will allow bootloaders to load a kernel specific device-tree.
The variable will not be exposed on ACPI based systems or if the environment variable fdtfile is not defined.
Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com
v4: Generalize the description of the content of $fdtfile. v3: Add documentation v2: Use a unique GUID to enable future U-Boot independent standardization. Do not try to add the variable on ACPI based systems.
doc/develop/uefi/uefi.rst | 14 ++++++++++++++ include/efi_loader.h | 5 +++++ lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ 3 files changed, 49 insertions(+)
diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst index fb16ac743a..702c490831 100644 --- a/doc/develop/uefi/uefi.rst +++ b/doc/develop/uefi/uefi.rst @@ -916,6 +916,20 @@ So our final format of the FilePathList[] is::
Loaded image - end node (0xff) - VenMedia - initrd_1 - [end node (0x01) - initrd_n ...] - end node (0xff)+EFI variable FdtFile +~~~~~~~~~~~~~~~~~~~~
+Ideally U-Boot would always expose a device-tree that can be used for booting +any operating systems. Unfortunately operating systems like Linux sometimes +break forward and backward compatibility. In this case there is a need to load +an operating system version specific device-tree.
+U-Boot has an environment variable fdtfile identifying the device-tree file to +load. The content of this variable is exposed as EFI variable Fdtfile, vendor +GUID d45dde69-3bd6-40e0-90d5-6b606aa57730. It contains the device-tree path +name as a NUL terminated ASCII string. On many architectures the file name is +preceded by a vendor directory ('vendor-directory/board-name.dtb').
Links
diff --git a/include/efi_loader.h b/include/efi_loader.h index e24410505f..146e7f1bce 100644 --- a/include/efi_loader.h +++ b/include/efi_loader.h @@ -152,6 +152,11 @@ static inline efi_status_t efi_launch_capsules(void) EFI_GUID(0x8108ac4e, 0x9f11, 0x4d59, \ 0x85, 0x0e, 0xe2, 0x1a, 0x52, 0x2c, 0x59, 0xb2)
+/* Vendor GUID for the FdtFile variable */ +#define VENDOR_FDTFILE_GUID \
EFI_GUID(0xd45dde69, 0x3bd6, 0x40e0, \0x90, 0xd5, 0x6b, 0x60, 0x6a, 0xa5, 0x77, 0x30)/* Use internal device tree when starting UEFI application */ #define EFI_FDT_USE_INTERNAL NULL
diff --git a/lib/efi_loader/efi_setup.c b/lib/efi_loader/efi_setup.c index e6de685e87..71bcde645b 100644 --- a/lib/efi_loader/efi_setup.c +++ b/lib/efi_loader/efi_setup.c @@ -17,6 +17,8 @@
efi_status_t efi_obj_list_initialized = OBJ_LIST_NOT_INITIALIZED;
+efi_guid_t vendor_fdtfile_guid = VENDOR_FDTFILE_GUID;
/*
- Allow unaligned memory access.
@@ -26,6 +28,27 @@ void __weak allow_unaligned(void) { }
+/**
- efi_init_fdtfile() - set EFI variable FdtFile
- Return: status code
- */
+static efi_status_t efi_init_fdtfile(void) +{
char *val;val = env_get("fdtfile");if (!val)return EFI_SUCCESS;return efi_set_variable_int(u"FdtFile",&vendor_fdtfile_guid,EFI_VARIABLE_BOOTSERVICE_ACCESS |EFI_VARIABLE_RUNTIME_ACCESS |EFI_VARIABLE_READ_ONLY,strlen(val) + 1, val, false);+}
/**
- efi_init_platform_lang() - define supported languages
@@ -250,6 +273,13 @@ efi_status_t efi_init_obj_list(void) if (ret != EFI_SUCCESS) goto out;
/* Define EFI variable FdtFile */if (!CONFIG_IS_ENABLED(GENERATE_ACPI_TABLE)) {ret = efi_init_fdtfile();if (ret != EFI_SUCCESS)goto out;}/* Indicate supported features */ ret = efi_init_os_indications(); if (ret != EFI_SUCCESS)-- 2.40.1
On Tue, 24 Oct 2023 at 09:20, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote:
Forward and backward compatibility of Linux kernel device-trees is sometimes missing. One solution approach is to load a kernel specific device-tree. This can either be done via a U-Boot scripts (like the one generated by Debian package flash-kernel or by a boot loader like GRUB. The boot loader approach currently requires to know the device-tree name before first boot which makes it unusable for generic images.
Expose the device-tree file name as EFI variable FdtFile. This will allow bootloaders to load a kernel specific device-tree.
The variable will not be exposed on ACPI based systems or if the environment variable fdtfile is not defined.
Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com
v4: Generalize the description of the content of $fdtfile. v3: Add documentation v2: Use a unique GUID to enable future U-Boot independent standardization. Do not try to add the variable on ACPI based systems.
doc/develop/uefi/uefi.rst | 14 ++++++++++++++ include/efi_loader.h | 5 +++++ lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ 3 files changed, 49 insertions(+)
diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst index fb16ac743a..702c490831 100644 --- a/doc/develop/uefi/uefi.rst +++ b/doc/develop/uefi/uefi.rst @@ -916,6 +916,20 @@ So our final format of the FilePathList[] is::
Loaded image - end node (0xff) - VenMedia - initrd_1 - [end node (0x01) - initrd_n ...] - end node (0xff)+EFI variable FdtFile +~~~~~~~~~~~~~~~~~~~~
+Ideally U-Boot would always expose a device-tree that can be used for booting +any operating systems. Unfortunately operating systems like Linux sometimes +break forward and backward compatibility. In this case there is a need to load +an operating system version specific device-tree.
+U-Boot has an environment variable fdtfile identifying the device-tree file to +load. The content of this variable is exposed as EFI variable Fdtfile, vendor +GUID d45dde69-3bd6-40e0-90d5-6b606aa57730. It contains the device-tree path +name as a NUL terminated ASCII string. On many architectures the file name is +preceded by a vendor directory ('vendor-directory/board-name.dtb').
Links
diff --git a/include/efi_loader.h b/include/efi_loader.h index e24410505f..146e7f1bce 100644 --- a/include/efi_loader.h +++ b/include/efi_loader.h @@ -152,6 +152,11 @@ static inline efi_status_t efi_launch_capsules(void) EFI_GUID(0x8108ac4e, 0x9f11, 0x4d59, \ 0x85, 0x0e, 0xe2, 0x1a, 0x52, 0x2c, 0x59, 0xb2)
+/* Vendor GUID for the FdtFile variable */ +#define VENDOR_FDTFILE_GUID \
EFI_GUID(0xd45dde69, 0x3bd6, 0x40e0, \0x90, 0xd5, 0x6b, 0x60, 0x6a, 0xa5, 0x77, 0x30)/* Use internal device tree when starting UEFI application */ #define EFI_FDT_USE_INTERNAL NULL
diff --git a/lib/efi_loader/efi_setup.c b/lib/efi_loader/efi_setup.c index e6de685e87..71bcde645b 100644 --- a/lib/efi_loader/efi_setup.c +++ b/lib/efi_loader/efi_setup.c @@ -17,6 +17,8 @@
efi_status_t efi_obj_list_initialized = OBJ_LIST_NOT_INITIALIZED;
+efi_guid_t vendor_fdtfile_guid = VENDOR_FDTFILE_GUID;
/*
- Allow unaligned memory access.
@@ -26,6 +28,27 @@ void __weak allow_unaligned(void) { }
+/**
- efi_init_fdtfile() - set EFI variable FdtFile
- Return: status code
- */
+static efi_status_t efi_init_fdtfile(void) +{
char *val;val = env_get("fdtfile");if (!val)return EFI_SUCCESS;return efi_set_variable_int(u"FdtFile",&vendor_fdtfile_guid,EFI_VARIABLE_BOOTSERVICE_ACCESS |EFI_VARIABLE_RUNTIME_ACCESS |EFI_VARIABLE_READ_ONLY,strlen(val) + 1, val, false);+}
/**
- efi_init_platform_lang() - define supported languages
@@ -250,6 +273,13 @@ efi_status_t efi_init_obj_list(void) if (ret != EFI_SUCCESS) goto out;
/* Define EFI variable FdtFile */if (!CONFIG_IS_ENABLED(GENERATE_ACPI_TABLE)) {ret = efi_init_fdtfile();if (ret != EFI_SUCCESS)goto out;}/* Indicate supported features */ ret = efi_init_os_indications(); if (ret != EFI_SUCCESS)-- 2.40.1
Reviewed-by: Ilias Apalodimas ilias.apalodimas@linaro.org
participants (5)
-
Heinrich Schuchardt -
Ilias Apalodimas -
Mark Kettenis -
Simon Glass -
Tom Rini