Re: [PATCH v1 1/2] rtc: cmos: Enable ACPI alarm if advertised in ACPI FADT

["Mario Limonciello (AMD) (kernel.org)" <superm1@kernel.org>]

On 3/14/2026 7:11 AM, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> If the ACPI_FADT_FIXED_RTC flag is unset, the platform is declaring that
> it supports the ACPI RTC fixed event which should be used instead of a
> dedicated CMOS RTC IRQ.  However, the driver only enables it when
> is_hpet_enabled() returns true, which is questionable because there is
> no clear connection between enabled HPET and signaling wakeup via the
> ACPI RTC fixed event (for instance, the latter can be expected to work
> on systems that don't include a functional HPET).
> 
> Moreover, since use_hpet_alarm() returns false if use_acpi_alarm is set,
> the ACPI RTC fixed event is effectively used instead of the HPET alarm
> if the latter is functional, but there is no particular reason why it
> could not be used otherwise.
> 
> Accordingly, on x86 systems with ACPI, set use_acpi_alarm if
> ACPI_FADT_FIXED_RTC is unset without looking at whether or not HPET is
> enabled.
> 
> Also, do the ACPI FADT check in use_acpi_alarm_quirks() before the DMI
> BIOS year checks which are more expensive and it's better to skip them
> if ACPI_FADT_FIXED_RTC is set.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

This makes sense to me.

Sorry for my delay, I kept on meaning to check a few machines and then 
more things came up and it fell lower.

I did check 3 generations of AMD machines and I don't expect any 
problems from this change.

Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>

> ---
>   drivers/rtc/rtc-cmos.c |    5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> --- a/drivers/rtc/rtc-cmos.c
> +++ b/drivers/rtc/rtc-cmos.c
> @@ -817,6 +817,9 @@ static void rtc_wake_off(struct device *
>   #ifdef CONFIG_X86
>   static void use_acpi_alarm_quirks(void)
>   {
> +	if (acpi_gbl_FADT.flags & ACPI_FADT_FIXED_RTC)
> +		return;
> +
>   	switch (boot_cpu_data.x86_vendor) {
>   	case X86_VENDOR_INTEL:
>   		if (dmi_get_bios_year() < 2015)
> @@ -830,8 +833,6 @@ static void use_acpi_alarm_quirks(void)
>   	default:
>   		return;
>   	}
> -	if (!is_hpet_enabled())
> -		return;
>   
>   	use_acpi_alarm = true;
>   }
> 
> 
>