erebion/coreboot
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

security/vboot: Back up CMOS data later boot phase

Browse source 
Introduce POSTPONE_SPI_ACCESS to save CMOS data in a later boot phase
to avoid flash access delay by other boot controllers.

Intel has pre-CPU boot controllers (e.g. CSE) which load non-CPU
firmwares. Boot-critical firmwares are loaded before CPU reset and
non-boot-critical firmwares are loaded during CPU boot. If another
controller accesses SPI to load firmwares, reading SPI by CPU is ok,
but writing to SPI for saving CMOS data can take ~30ms sometimes.
Saving CMOS data usually takes less than 1ms.


Before this change, sometimes it delays like below:
BS: callback (0x7386f908) @ src/security/vboot/vbnv_cmos.c:122 (32 ms)
After this change, the delay is less than 1 ms:
BS: callback (0x7386f908) @ src/security/vboot/vbnv_cmos.c:122 (0 ms)

TEST
1. Enable DEBUG_BOOT_STATE
2. Check time
BS: callback (0x7386f908) @ src/security/vboot/vbnv_cmos.c:120 (0 ms)

Signed-off-by: Wonkyu Kim <wonkyu.kim@intel.com>
Change-Id: I8836c14601beb56c614605b9840c8506d6d8536c
Reviewed-on: https://review.coreboot.org/c/coreboot/+/87738
Reviewed-by: Subrata Banik <subratabanik@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
This commit is contained in:
Wonkyu Kim 2025-05-16 01:39:36 -07:00 • committed by Matt DeVillier
commit bf330f2dd0
2 changed files with 14 additions and 0 deletions
Download patch file Download diff file Expand all files Collapse all files

9
src/Kconfig
View file

@ -1563,3 +1563,12 @@ config HAVE_RAMSTAGE
config SEPARATE_ROMSTAGE
default y
config POSTPONE_SPI_ACCESS
bool
help
Enable this option to postpone SPI access to later boot phase
(BS_PAYLOAD_BOOT) to prevent flash write access delays caused by
simultaneous accesses from other SPI masters like CSE. This symptom
was found in Intel SoCs (Panther Lake and Wildcat Lake) but it can be
used other SOCs.

5
src/security/vboot/vbnv_cmos.c
View file

@ -115,5 +115,10 @@ static void back_up_vbnv_cmos(void *unused)
/* Save to flash, will only be saved if different. */
save_vbnv_flash(vbnv_cmos);
}
#if CONFIG(POSTPONE_SPI_ACCESS)
BOOT_STATE_INIT_ENTRY(BS_PAYLOAD_LOAD, BS_ON_EXIT, back_up_vbnv_cmos, NULL);
#else
BOOT_STATE_INIT_ENTRY(BS_POST_DEVICE, BS_ON_EXIT, back_up_vbnv_cmos, NULL);
#endif
#endif