From b6e1007e27d695985950b0284ea56680afab42e3 Mon Sep 17 00:00:00 2001 From: Yu-Ping Wu Date: Wed, 17 Jul 2024 11:01:15 +0800 Subject: 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 Reviewed-on: https://review.coreboot.org/c/coreboot/+/83495 Reviewed-by: Matt DeVillier Reviewed-by: Karthik Ramasubramanian Tested-by: build bot (Jenkins) --- src/soc/amd/common/vboot/vbnv_cmos.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/src/soc/amd/common/vboot/vbnv_cmos.c b/src/soc/amd/common/vboot/vbnv_cmos.c index 5baf923939..31c8128d65 100644 --- a/src/soc/amd/common/vboot/vbnv_cmos.c +++ b/src/soc/amd/common/vboot/vbnv_cmos.c @@ -3,6 +3,12 @@ #include #include +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 */ -- cgit v1.2.3