Re: [RESEND RFC PATCH v3] rtc: Fix the AltCentury value on AMD/Hygon platform

From: Alexandre Belloni
Date: Tue Oct 15 2019 - 04:27:26 EST


Oh come on, you sent that patch only a week ago and v2 had a so obvious
mistake that my trust in your code quality is now very low.

On 15/10/2019 16:08:27+0800, Jinke Fan wrote:
> When using following operations:
> date -s "21190910 19:20:00"
> hwclock -w
> to change date from 2019 to 2119 for test, it will fail on Hygon
> Dhyana and AMD Zen CPUs, while the same operations run ok on Intel i7
> platform.
>
> 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.
>
> Test results on AMD/Hygon machine show that it works as expected.
>
> Reference:
> https://www.amd.com/system/files/TechDocs/51192_Bolton_FCH_RRG.pdf
> section: 3.13 Real Time Clock (RTC)
>
> Reported-by: kbuild test robot <lkp@xxxxxxxxx>
> Signed-off-by: Jinke Fan <fanjinke@xxxxxxxx>
> ---
>
> v2->v3:
> - Make the changes only relevant to AMD/Hygon.
>
> v1->v2:
> - Fix the compile errors on sparc64/alpha platform.
>
> drivers/rtc/rtc-mc146818-lib.c | 11 ++++++++++-
> include/linux/mc146818rtc.h | 6 ++++++
> 2 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c
> index 2ecd8752b088..70502881785d 100644
> --- a/drivers/rtc/rtc-mc146818-lib.c
> +++ b/drivers/rtc/rtc-mc146818-lib.c
> @@ -172,7 +172,16 @@ 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);
> +
> +#ifdef CONFIG_X86
> + if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
> + boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
> + CMOS_WRITE((save_freq_select & (~RTC_DV0)), RTC_FREQ_SELECT);
> + else
> + CMOS_WRITE((save_freq_select | RTC_DIV_RESET2), RTC_FREQ_SELECT);
> +#else
> + CMOS_WRITE((save_freq_select | RTC_DIV_RESET2), RTC_FREQ_SELECT);
> +#endif
>
> #ifdef CONFIG_MACH_DECSTATION
> CMOS_WRITE(real_yrs, RTC_DEC_YEAR);
> diff --git a/include/linux/mc146818rtc.h b/include/linux/mc146818rtc.h
> index 0661af17a758..7066a7bced61 100644
> --- a/include/linux/mc146818rtc.h
> +++ b/include/linux/mc146818rtc.h
> @@ -86,6 +86,12 @@ 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
> +
> +#ifdef CONFIG_X86
> + /* DV0 = 0 selects Bank 0, DV0 = 1 selects Bank 1 on AMD/Hygon platform */
> +# define RTC_DV0 0x10
> +#endif
> +
> /* Periodic intr. / Square wave rate select. 0=none, 1=32.8kHz,... 15=2Hz */
> # define RTC_RATE_SELECT 0x0F
>
> --
> 2.17.1
>

--
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com