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

[Alexandre Belloni <alexandre.belloni@bootlin.com>]

On 14/03/2026 13:11:20+0100, 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>

Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

> ---
>  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;
>  }
> 
> 
> 

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