Felix Held has submitted this change. ( https://review.coreboot.org/c/coreboot/+/83495?usp=email )
Change subject: soc/amd: Ensure bank 0 is selected before accessing VBNV in CMOS ......................................................................
soc/amd: Ensure bank 0 is selected before accessing VBNV in CMOS
In AMD platforms, the bit 4 of CMOS's Register A (0x0a) is DV0 bank selection (0 for Bank 0; 1 for Bank 1) [1]. Since the MC146818 driver accesses VBNV via Bank 0, the bit must be cleared before we can save VBNV to CMOS in verstage.
Usually there's no problem with that, because the Register A is configured in cmos_init() in ramstage. However, if CMOS has lost power, then in the first boot after that, the bit may contain arbitrary data in verstage. If that bit happens to be 1, then CMOS writes in verstage will fail.
To fix the problem, define vbnv_platform_init_cmos() to call cmos_init(0), which will configure the Register A and therefore allow saving VBNV to CMOS in verstage.
[1] 48751_16h_bkdg.pdf
BUG=b:346716300 TEST=CMOS writes succeeded in verstage after battery cutoff BRANCH=skyrim
Change-Id: Idf167387b403be1977ebc08daa1f40646dd8c83f Signed-off-by: Yu-Ping Wu yupingso@chromium.org Reviewed-on: https://review.coreboot.org/c/coreboot/+/83495 Reviewed-by: Matt DeVillier matt.devillier@amd.corp-partner.google.com Reviewed-by: Karthik Ramasubramanian kramasub@google.com Tested-by: build bot (Jenkins) no-reply@coreboot.org --- M src/soc/amd/common/vboot/vbnv_cmos.c 1 file changed, 6 insertions(+), 0 deletions(-)
Approvals: Karthik Ramasubramanian: Looks good to me, approved Matt DeVillier: Looks good to me, approved build bot (Jenkins): Verified
diff --git a/src/soc/amd/common/vboot/vbnv_cmos.c b/src/soc/amd/common/vboot/vbnv_cmos.c index 5baf923..31c8128 100644 --- a/src/soc/amd/common/vboot/vbnv_cmos.c +++ b/src/soc/amd/common/vboot/vbnv_cmos.c @@ -3,6 +3,12 @@ #include <security/vboot/vbnv.h> #include <pc80/mc146818rtc.h>
+void vbnv_platform_init_cmos(void) +{ + /* The 0 argument tells cmos_init not to update CMOS unless it is invalid. */ + cmos_init(0); +} + int vbnv_cmos_failed(void) { /* If CMOS power has failed, the century will be set to 0xff */