From: Mario Limonciello mario.limonciello@amd.com
[ Upstream commit 3ae8fd41573af4fb3a490c9ed947fc936ba87190 ]
Setting the century forward has been failing on AMD platforms. There was a previous attempt at fixing this for family 0x17 as part of commit 7ad295d5196a ("rtc: Fix the AltCentury value on AMD/Hygon platform") but this was later reverted due to some problems reported that appeared to stem from an FW bug on a family 0x17 desktop system.
The same comments mentioned in the previous commit continue to apply to the newer platforms as well.
``` MC146818 driver use function mc146818_set_time() to set register RTC_FREQ_SELECT(RTC_REG_A)'s bit4-bit6 field which means divider stage reset value on Intel platform to 0x7.
While AMD/Hygon RTC_REG_A(0Ah)'s bit4 is defined as DV0 [Reference]: DV0 = 0 selects Bank 0, DV0 = 1 selects Bank 1. Bit5-bit6 is defined as reserved.
DV0 is set to 1, it will select Bank 1, which will disable AltCentury register(0x32) access. As UEFI pass acpi_gbl_FADT.century 0x32 (AltCentury), the CMOS write will be failed on code: CMOS_WRITE(century, acpi_gbl_FADT.century).
Correct RTC_REG_A bank select bit(DV0) to 0 on AMD/Hygon CPUs, it will enable AltCentury(0x32) register writing and finally setup century as expected. ```
However in closer examination the change previously submitted was also modifying bits 5 & 6 which are declared reserved in the AMD documentation. So instead modify just the DV0 bank selection bit.
Being cognizant that there was a failure reported before, split the code change out to a static function that can also be used for exclusions if any regressions such as Mikhail's pop up again.
Cc: Jinke Fan fanjinke@hygon.cn Cc: Mikhail Gavrilov mikhail.v.gavrilov@gmail.com Link: https://lore.kernel.org/all/CABXGCsMLob0DC25JS8wwAYydnDoHBSoMh2_YLPfqm3TTvDE... Link: https://www.amd.com/system/files/TechDocs/51192_Bolton_FCH_RRG.pdf Signed-off-by: Raul E Rangel rrangel@chromium.org Signed-off-by: Mario Limonciello mario.limonciello@amd.com Signed-off-by: Alexandre Belloni alexandre.belloni@bootlin.com Link: https://lore.kernel.org/r/20220111225750.1699-1-mario.limonciello@amd.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/rtc/rtc-mc146818-lib.c | 16 +++++++++++++++- include/linux/mc146818rtc.h | 2 ++ 2 files changed, 17 insertions(+), 1 deletion(-)
diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c index ae9f131b43c0..05f251ba6a3a 100644 --- a/drivers/rtc/rtc-mc146818-lib.c +++ b/drivers/rtc/rtc-mc146818-lib.c @@ -176,6 +176,17 @@ int mc146818_get_time(struct rtc_time *time) } EXPORT_SYMBOL_GPL(mc146818_get_time);
+/* AMD systems don't allow access to AltCentury with DV1 */ +static bool apply_amd_register_a_behavior(void) +{ +#ifdef CONFIG_X86 + if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD || + boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) + return true; +#endif + return false; +} + /* Set the current date and time in the real time clock. */ int mc146818_set_time(struct rtc_time *time) { @@ -247,7 +258,10 @@ int mc146818_set_time(struct rtc_time *time) save_control = CMOS_READ(RTC_CONTROL); CMOS_WRITE((save_control|RTC_SET), RTC_CONTROL); save_freq_select = CMOS_READ(RTC_FREQ_SELECT); - CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT); + if (apply_amd_register_a_behavior()) + CMOS_WRITE((save_freq_select & ~RTC_AMD_BANK_SELECT), RTC_FREQ_SELECT); + else + CMOS_WRITE((save_freq_select|RTC_DIV_RESET2), RTC_FREQ_SELECT);
#ifdef CONFIG_MACH_DECSTATION CMOS_WRITE(real_yrs, RTC_DEC_YEAR); diff --git a/include/linux/mc146818rtc.h b/include/linux/mc146818rtc.h index 808bb4cee230..b0da04fe087b 100644 --- a/include/linux/mc146818rtc.h +++ b/include/linux/mc146818rtc.h @@ -86,6 +86,8 @@ struct cmos_rtc_board_info { /* 2 values for divider stage reset, others for "testing purposes only" */ # define RTC_DIV_RESET1 0x60 # define RTC_DIV_RESET2 0x70 + /* In AMD BKDG bit 5 and 6 are reserved, bit 4 is for select dv0 bank */ +# define RTC_AMD_BANK_SELECT 0x10 /* Periodic intr. / Square wave rate select. 0=none, 1=32.8kHz,... 15=2Hz */ # define RTC_RATE_SELECT 0x0F