Re: [PATCH] arm: init: add an option to use FDT from previous bootloader

Hi Caleb,

On Tue, 24 Oct 2023 at 04:32, Caleb Connolly caleb.connolly@linaro.org wrote:

Add a new config option to allow u-boot to reuse the FDT provided by the

U-Boot (please fix throughout)

previous stage bootloader when available.

On some boards the previous stage bootloader can populate platform-specific parts of the devicetree such as the memory node, this allows us to avoid hardcoding it in u-boot and instead determine it dynamically at runtime.

Signed-off-by: Caleb Connolly caleb.connolly@linaro.org

This patch will improve generic support for Qualcomm boards by enabling us to configure the memory map at runtime rather than having hardcoded maps on a per-device basis. I've gone for this approach initially to try and avoid introducing board specific code where possible, but I'm happy to rework this into mach-snapdragon if that's preferred.

Do you think it could use bloblist instead? I did send a patch to use the FDT in the bloblist:

https://patchwork.ozlabs.org/project/uboot/patch/20230926141514.2101787-40-s...

Regards, Simon

---

base-commit: e65b5d35c9116485366bb08138043d51220551da

// Caleb (they/them)

arch/arm/lib/save_prev_bl_data.c | 7 +++++++ boot/Kconfig | 10 ++++++++++ include/init.h | 9 +++++++++ lib/fdtdec.c | 7 ++++++- 4 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/arch/arm/lib/save_prev_bl_data.c b/arch/arm/lib/save_prev_bl_data.c index f7b23faf0d66..b0608502535e 100644 --- a/arch/arm/lib/save_prev_bl_data.c +++ b/arch/arm/lib/save_prev_bl_data.c @@ -45,6 +45,13 @@ bool is_addr_accessible(phys_addr_t addr) return false; }

+phys_addr_t get_prev_bl_fdt_addr(void) +{

•   if (!is_addr_accessible((phys_addr_t)reg0))
  

•           return 0;
  

•   return reg0;
  

+}

int save_prev_bl_data(void) { struct fdt_header *fdt_blob; diff --git a/boot/Kconfig b/boot/Kconfig index a01e6cb8aafe..c127ba254589 100644 --- a/boot/Kconfig +++ b/boot/Kconfig @@ -1599,6 +1599,16 @@ config SAVE_PREV_BL_INITRAMFS_START_ADDR If no initramfs was provided by previous bootloader, no env variables will be created.

+config USE_PREV_BL_FDT

•   depends on SAVE_PREV_BL_FDT_ADDR && !OF_BOARD
  

•   bool "Use the FDT provided by the previous stage bootloader"
  

•   help
  

•     When u-boot is chain-loaded from a previous bootloader, enable this option
  

•     to use the FDT provided by the previous bootloader instead of any built-in
  

•     to u-boot.
  

•     If no FDT was available, u-boot will fall back to its internal FDT.
  

menu "Configuration editor"

config CEDIT diff --git a/include/init.h b/include/init.h index 4e7fe26c2004..58604cd98758 100644 --- a/include/init.h +++ b/include/init.h @@ -168,6 +168,15 @@ defined(CONFIG_SAVE_PREV_BL_FDT_ADDR)

• Return: 0 if ok; -ENODATA on error

*/ int save_prev_bl_data(void);

+/**

• • get_prev_bl_fdt_addr - When u-boot is chainloaded, get the address
• • of the FDT passed by the previous bootloader.
• • Return: the address of the FDT passed by the previous bootloader
• • or 0 if not found.
• */

+phys_addr_t get_prev_bl_fdt_addr(void); #endif

/** diff --git a/lib/fdtdec.c b/lib/fdtdec.c index 7a6916764835..85425f2dc1ee 100644 --- a/lib/fdtdec.c +++ b/lib/fdtdec.c @@ -1222,7 +1222,7 @@ static int uncompress_blob(const void *src, ulong sz_src, void **dstp) */ static void *fdt_find_separate(void) {

•   void *fdt_blob = NULL;
  

•   void *fdt_blob = NULL, *prevbl_fdt_blob;
  
    if (IS_ENABLED(CONFIG_SANDBOX))
            return NULL;
  

@@ -1234,6 +1234,11 @@ static void *fdt_find_separate(void) else fdt_blob = (ulong *)__bss_end; #else +#if defined(CONFIG_USE_PREV_BL_FDT)

•   prevbl_fdt_blob = (void *)get_prev_bl_fdt_addr();
  

•   if (prevbl_fdt_blob)
  

•           return prevbl_fdt_blob;
  

+#endif /* FDT is at end of image */ fdt_blob = (ulong *)_end;

Regards, SImon