[PATCH v3] ata: ahci: Do not check ACPI_FADT_LOW_POWER_S0

[PATCH v3] ata: ahci: Do not check ACPI_FADT_LOW_POWER_S0

[Rafael J. Wysocki]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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, replace the ACPI_FADT_LOW_POWER_S0 check in
ahci_update_initial_lpm_policy() with pm_suspend_default_s2idle()
which is more general and also takes the user's preference into
account and drop the CONFIG_ACPI #ifdef around it that is not necessary
any more.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---

v2 -> v3:
   * Use pm_suspend_default_s2idle() instead of the check being dropped.
   * Update the changelog.

v1 -> v2:
   * Adjust subject (Damien).
   * Drop #ifdef CONFIG_ACPI that is not necessary any more (Mario).
   * Update the changelog.

---
 drivers/ata/ahci.c |    5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

Index: linux-pm/drivers/ata/ahci.c
===================================================================
--- linux-pm.orig/drivers/ata/ahci.c
+++ linux-pm/drivers/ata/ahci.c
@@ -1609,15 +1609,12 @@ static void ahci_update_initial_lpm_poli
 		goto update_policy;
 	}
 
-#ifdef CONFIG_ACPI
-	if (policy > ATA_LPM_MED_POWER &&
-	    (acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0)) {
+	if (policy > ATA_LPM_MED_POWER && pm_suspend_default_s2idle()) {
 		if (hpriv->cap & HOST_CAP_PART)
 			policy = ATA_LPM_MIN_POWER_WITH_PARTIAL;
 		else if (hpriv->cap & HOST_CAP_SSC)
 			policy = ATA_LPM_MIN_POWER;
 	}
-#endif
 
 update_policy:
 	if (policy >= ATA_LPM_UNKNOWN && policy <= ATA_LPM_MIN_POWER)

Re: [PATCH v3] ata: ahci: Do not check ACPI_FADT_LOW_POWER_S0

[Limonciello, Mario]

On 8/25/2022 13:47, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> 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, replace the ACPI_FADT_LOW_POWER_S0 check in
> ahci_update_initial_lpm_policy() with pm_suspend_default_s2idle()
> which is more general and also takes the user's preference into
> account and drop the CONFIG_ACPI #ifdef around it that is not necessary
> any more.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>

> ---
> 
> v2 -> v3:
>     * Use pm_suspend_default_s2idle() instead of the check being dropped.
>     * Update the changelog.
> 
> v1 -> v2:
>     * Adjust subject (Damien).
>     * Drop #ifdef CONFIG_ACPI that is not necessary any more (Mario).
>     * Update the changelog.
> 
> ---
>   drivers/ata/ahci.c |    5 +----
>   1 file changed, 1 insertion(+), 4 deletions(-)
> 
> Index: linux-pm/drivers/ata/ahci.c
> ===================================================================
> --- linux-pm.orig/drivers/ata/ahci.c
> +++ linux-pm/drivers/ata/ahci.c
> @@ -1609,15 +1609,12 @@ static void ahci_update_initial_lpm_poli
>   		goto update_policy;
>   	}
>   
> -#ifdef CONFIG_ACPI
> -	if (policy > ATA_LPM_MED_POWER &&
> -	    (acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0)) {
> +	if (policy > ATA_LPM_MED_POWER && pm_suspend_default_s2idle()) {
>   		if (hpriv->cap & HOST_CAP_PART)
>   			policy = ATA_LPM_MIN_POWER_WITH_PARTIAL;
>   		else if (hpriv->cap & HOST_CAP_SSC)
>   			policy = ATA_LPM_MIN_POWER;
>   	}
> -#endif
>   
>   update_policy:
>   	if (policy >= ATA_LPM_UNKNOWN && policy <= ATA_LPM_MIN_POWER)
> 
> 
> 

Re: [PATCH v3] ata: ahci: Do not check ACPI_FADT_LOW_POWER_S0

[Damien Le Moal]

On 8/26/22 03:47, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> 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, replace the ACPI_FADT_LOW_POWER_S0 check in
> ahci_update_initial_lpm_policy() with pm_suspend_default_s2idle()
> which is more general and also takes the user's preference into
> account and drop the CONFIG_ACPI #ifdef around it that is not necessary
> any more.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Applied to for-6.1. Thanks !

> ---
> 
> v2 -> v3:
>    * Use pm_suspend_default_s2idle() instead of the check being dropped.
>    * Update the changelog.
> 
> v1 -> v2:
>    * Adjust subject (Damien).
>    * Drop #ifdef CONFIG_ACPI that is not necessary any more (Mario).
>    * Update the changelog.
> 
> ---
>  drivers/ata/ahci.c |    5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> Index: linux-pm/drivers/ata/ahci.c
> ===================================================================
> --- linux-pm.orig/drivers/ata/ahci.c
> +++ linux-pm/drivers/ata/ahci.c
> @@ -1609,15 +1609,12 @@ static void ahci_update_initial_lpm_poli
>  		goto update_policy;
>  	}
>  
> -#ifdef CONFIG_ACPI
> -	if (policy > ATA_LPM_MED_POWER &&
> -	    (acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0)) {
> +	if (policy > ATA_LPM_MED_POWER && pm_suspend_default_s2idle()) {
>  		if (hpriv->cap & HOST_CAP_PART)
>  			policy = ATA_LPM_MIN_POWER_WITH_PARTIAL;
>  		else if (hpriv->cap & HOST_CAP_SSC)
>  			policy = ATA_LPM_MIN_POWER;
>  	}
> -#endif
>  
>  update_policy:
>  	if (policy >= ATA_LPM_UNKNOWN && policy <= ATA_LPM_MIN_POWER)
> 
> 
> 


-- 
Damien Le Moal
Western Digital Research