Re: [PATCH] Add support for SPL MMC load redundant U-Boot

20 Jul 2023

Hi Ayrton,
On 19.07.23 15:38, Ayrton Leyssens wrote:
...
Hi Stefano
...
-----Original Message-----
From: Stefano Babic sbabic@denx.de
Sent: Wednesday, July 19, 2023 11:57 AM
To: Ayrton Leyssens ayrton.leyssens@scioteq.com; u-boot@lists.denx.de
Subject: Re: [PATCH] Add support for SPL MMC load redundant U-Boot
Hi Ayrton,
On 19.07.23 11:38, Ayrton Leyssens wrote:
...
From 99512830410551132e8f7577615b3af4f5f1c137 Mon Sep 17 00:00:00
2001
From: Ayrton Leyssens ayrton.leyssens@scioteq.com
Date: Wed, 19 Jul 2023 11:27:19 +0200
Subject: [PATCH Add support for SPL mmc load redundant U-Boot
This patch adds support for loading a redundant / second U-Boot from a
MMC.
...
In some cases you want to update U-Boot, to have a "selectable"
bootloader and keep the "old" and "new" one.
...
In this patch we use the environment for a user-defined variable.
Maybe this could be extended to some other ways as well.
I find the selection based on an environment variable quite weak. A wrong
value could lead to unbootable device. IMHO the selection should be done in
a way similar as what we have for the environment itself, that means the
information if a u-boot image is valid or not should be inside the image itself.
For example this is true in case u-boot is packed inside a fitImage.
Maybe my word choice is not that clear.
I do not mean it as a redundant U-Boot in case the first choice fails.
More as like, a selectable U-Boot.
It was clear :-)
...
The U-Boot could be selected by the user within U-Boot, or a higher level OS by setting the environment variable.
This in case of a complete redundant system (with exception of the MLO) in which the user makes sure a software update goes well.
If the user verifies the U-Boot is written well,
Rather experience learns that if an image was well written, it does not 
mean that all devices in fields will boot. On upper layers (kernel, 
rootfs,app) it is usual to have a fallback in case something is going 
wrong. In this case, it does not happen, and the usage of an environment 
can be misuesed. It is true, this is done for kernel and rootfs, too, 
but in those cases we still have the bootloader making a decision and 
running a fallback, if something is going wrong. The feature in the 
patch is already available if u-boot is written on the mmcblkbootX 
partition, and after writing successfully the new u-boot image, user 
space will toggle the hardware partitions via the extCSD register in the 
eMMC. Even in that case, there is no fallback.
...
he will toggle the environment variable and as such boot the whole 'B' side of the software chain.
Next update writes over the 'A' side and toggles to boot the 'A' side next.
...
A simple selection is not sufficient, there should be a mechanism like for the
environmant to fallback to the other partition if the chosen is not working or
at least, integrity check is broken.
I agree, for a complete redundant U-Boot, this is not sufficient.
At least, this could be the first step to such system.
My idea for a full redundant u-boot is quite different. If u-boot is put 
into a fit, SPL can check the integrity of image and via bootcounter in 
SPL can even switch to the old one if something is wrong, of course by 
enabling watchdog in SPL. This feature is in my opinion already 
available on eMMC by switching the hardware boot partitions.
Best regards,
Stefano
...
...
Best regards,
Stefano
...
Signed-off-by: Ayrton Leyssens ayrton.leyssens@scioteq.com
common/spl/Kconfig   | 29 +++++++++++++++++++++++++++++
common/spl/spl_mmc.c | 10 ++++++++++
2 files changed, 39 insertions(+)

diff --git a/common/spl/Kconfig b/common/spl/Kconfig index
bee231b583..2c0ffd4363 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -824,6 +824,25 @@ config SYS_MMCSD_FS_BOOT
                   Enable MMC FS Boot mode. Partition is selected by option
                   SYS_MMCSD_FS_BOOT_PARTITION.
+config SYS_MMCSD_FS_BOOT_PARTITION_FAILSAFE

        bool "Use MMC Boot Partition Failsafe"


        depends on SYS_MMCSD_FS_BOOT


        depends on SPL_ENV_SUPPORT


        default false


        help


          Use a redundant partition to load U-Boot from.




+config SYS_MMCSD_FS_BOOT_PARTITION_SELECTOR

        string "MMC Boot Partition Selector"


        depends on SYS_MMCSD_FS_BOOT


        depends on SYS_MMCSD_FS_BOOT_PARTITION_FAILSAFE


        default ""


        help


          Environment variable in U-Boot to use for the partition selection


          to boot U-Boot from.


          A 1 selects the "normal" partition, any other value selects the


          redundant partition.




config SYS_MMCSD_FS_BOOT_PARTITION
                 int "MMC Boot Partition"
                 depends on SYS_MMCSD_FS_BOOT @@ -833,6 +852,16 @@
config SYS_MMCSD_FS_BOOT_PARTITION
                   used in fs mode.
                   Use -1 as a special value to use the first bootable partition.
+config SYS_MMCSD_FS_BOOT_PARTITION_REDUNDANT

        int "MMC Boot Partition Redundant"


        depends on SYS_MMCSD_FS_BOOT


        depends on SYS_MMCSD_FS_BOOT_PARTITION_FAILSAFE


        default 2


        help


          Redundant Partition on the MMC to load U-Boot from when the



MMC is being
...

          used in fs mode.


          Use -1 as a special value to use the first bootable partition.




config SPL_MMC_TINY
                 bool "Tiny MMC framework in SPL"
                 depends on SPL_MMC
diff --git a/common/spl/spl_mmc.c b/common/spl/spl_mmc.c index
a665091b00..bf804fabcc 100644
--- a/common/spl/spl_mmc.c
+++ b/common/spl/spl_mmc.c
@@ -10,6 +10,7 @@
#include <log.h>
#include <part.h>
#include <spl.h>
+#include <env.h>
#include <linux/compiler.h>
#include <errno.h>
#include <asm/u-boot.h>
@@ -281,6 +282,7 @@ static int spl_mmc_do_fs_boot(struct
spl_image_info *spl_image,
...
             int err = -ENOSYS;
              __maybe_unused int partition =

CONFIG_SYS_MMCSD_FS_BOOT_PARTITION;

        __maybe_unused int env_partition_selector = 0;

#if CONFIG_SYS_MMCSD_FS_BOOT_PARTITION == -1
               {

@@ -303,7 +305,15 @@ static int spl_mmc_do_fs_boot(struct
spl_image_info *spl_image,
...
                             }
             }

#endif
+#ifdef CONFIG_SYS_MMCSD_FS_BOOT_PARTITION_FAILSAFE

        env_init();


        env_relocate();


        env_partition_selector =



+env_get_ulong(CONFIG_SYS_MMCSD_FS_BOOT_PARTITION_SELECTOR,
10, 0);
...


        if (env_partition_selector != 1)


                        partition =



+CONFIG_SYS_MMCSD_FS_BOOT_PARTITION_REDUNDANT;
+#endif
#ifdef CONFIG_SPL_FS_FAT
                 if (!spl_start_uboot()) {
                                 err = spl_load_image_fat_os(spl_image,
bootdev, mmc_get_blk_desc(mmc),
--
2.25.1
--
===========
DENX Software Engineering GmbH,        Managing Director: Erika Unter
HRB 165235 Munich,   Office: Kirchenstr.5, 82194 Groebenzell, Germany
Phone: +49-8142-66989-53 Fax: +49-8142-66989-80 Email: sbabic@denx.de
==========================================================
===========
-- 
=====================================================================
DENX Software Engineering GmbH,        Managing Director: Erika Unter
HRB 165235 Munich,   Office: Kirchenstr.5, 82194 Groebenzell, Germany
Phone: +49-8142-66989-53 Fax: +49-8142-66989-80 Email: sbabic@denx.de
=====================================================================


    