On 2022/08/24 10:29, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
The patch title should be "ata: ahci: ..."
>
> The ACPI_FADT_LOW_POWER_S0 flag merely means that it is better to
> use low-power S0 idle on the given platform than S3 (provided that
> the latter is supported) and it doesn't preclude using either of
> them (which of them will be used depends on the choices made by user
> space).
>
> For this reason, there is no benefit from checking that flag in
> ahci_update_initial_lpm_policy().
>
> First off, it cannot be a bug to do S3 with policy set to either
> ATA_LPM_MIN_POWER_WITH_PARTIAL or ATA_LPM_MIN_POWER, because S3 can be
> used on systems with ACPI_FADT_LOW_POWER_S0 set and it must work if
> really supported, so the ACPI_FADT_LOW_POWER_S0 check is not needed to
> protect the S3-capable systems from failing.
>
> Second, suspend-to-idle can be carried out on a system with
> ACPI_FADT_LOW_POWER_S0 unset and it is expected to work, so if setting
> policy to either ATA_LPM_MIN_POWER_WITH_PARTIAL or ATA_LPM_MIN_POWER is
> needed to handle that case correctly, it should be done regardless of
> the ACPI_FADT_LOW_POWER_S0 value.
>
> Accordingly, drop the ACPI_FADT_LOW_POWER_S0 check from
> ahci_update_initial_lpm_policy().
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
> drivers/ata/ahci.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> Index: linux-pm/drivers/ata/ahci.c
> ===================================================================
> --- linux-pm.orig/drivers/ata/ahci.c
> +++ linux-pm/drivers/ata/ahci.c
> @@ -1610,8 +1610,7 @@ static void ahci_update_initial_lpm_poli
> }
>
> #ifdef CONFIG_ACPI
> - if (policy > ATA_LPM_MED_POWER &&
> - (acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0)) {
> + if (policy > ATA_LPM_MED_POWER) {
> if (hpriv->cap & HOST_CAP_PART)
> policy = ATA_LPM_MIN_POWER_WITH_PARTIAL;
> else if (hpriv->cap & HOST_CAP_SSC)
>
>
>
--
Damien Le Moal
Western Digital Research
