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authorMario Limonciello <mario.limonciello@amd.com>2022-01-11 16:57:50 -0600
committerAlexandre Belloni <alexandre.belloni@bootlin.com>2022-03-29 22:45:31 +0200
commit3ae8fd41573af4fb3a490c9ed947fc936ba87190 (patch)
tree920fccf101af67671604f25d844def218ca3016e /drivers/rtc
parent81c2f059ab90b221931e78503c80dcd8fbadac53 (diff)
rtc: mc146818-lib: Fix the AltCentury for AMD platforms
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-Zw@mail.gmail.com/ 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
Diffstat (limited to 'drivers/rtc')
-rw-r--r--drivers/rtc/rtc-mc146818-lib.c16
1 files changed, 15 insertions, 1 deletions
diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c
index 562f99b664a2..522449b25921 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)
{
@@ -249,7 +260,10 @@ 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);