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src/lib: use RO CBFS file as fw_config source

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The FW_CONFIG_SOURCE_CBFS option serves as a backup for
FW_CONFIG_SOURCE_CHROMEEC_CBI, utilizing variables stored in CBFS.
When using ChromeEC CBI as the firmware configuration source,
changes to fw_config values can be made without updating the firmware
image. However, using CBFS as the configuration source requires
resigning the firmware because the current implementation reads from
the RW firmware region (FW_MAIN_A/B), necessitating resigning for
updates.  To avoid this step, the code should be modified to use the
RO CBFS for fw_config values instead of the RW (Read-Write) CBFS.

TEST:
1. Add FW_CONFIG_SOURCE_CBFS in board Kconfig and build image
2. Modify fw_config value by cbfstool with built image
3. flash and boot up system
4. Check updated fw_config value

Signed-off-by: Wonkyu Kim <wonkyu.kim@intel.com>
Change-Id: I4710a1043fe75888d2dcaee98c6957e6bd639be9
Reviewed-on: https://review.coreboot.org/c/coreboot/+/86943
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Cliff Huang <cliff.huang@intel.com>
Reviewed-by: Jamie Ryu <jamie.m.ryu@intel.com>
Reviewed-by: Jérémy Compostella <jeremy.compostella@intel.com>
Reviewed-by: Subrata Banik <subratabanik@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Bora Guvendik <bora.guvendik@intel.com>
This commit is contained in:
Wonkyu Kim 2025-03-20 15:23:43 -07:00 • committed by Jérémy Compostella
commit aa3da6e785
1 changed files with 2 additions and 2 deletions
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4
src/lib/fw_config.c
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@ -34,8 +34,8 @@ uint64_t fw_config_get(void)
/* Look in CBFS to allow override of value. */
if (CONFIG(FW_CONFIG_SOURCE_CBFS) && fw_config_value == UNDEFINED_FW_CONFIG) {
if (cbfs_load(CONFIG_CBFS_PREFIX "/fw_config", &fw_config_value,
sizeof(fw_config_value)) != sizeof(fw_config_value))
if (cbfs_ro_load(CONFIG_CBFS_PREFIX "/fw_config", &fw_config_value,
sizeof(fw_config_value)) != sizeof(fw_config_value))
printk(BIOS_WARNING, "%s: Could not get fw_config from CBFS\n",
__func__);
else