Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
IronPort-SDR: f8jxblJ2mg8PH953xgwKGfXFKeGiyBsuAGXDodxT0/bq48mTJpOEt2ITfO0L7mqIfxILXDuXvp
 mJ4fMDkyORmHAhvdDLzbgvCJSh+eu8XCtJYBly5MzImuRWeql+jfSgw6nyxxUCq08KJ617Y+/n
 0HCbslOwyw60taeuRx1NRck+zCWpiQQErXvZy+Pu61vHVH9z4rPWo4zTwqp3ntWYZVx+wXV12l
 fbwV5lxwPJaOa2NOZIOrvsmViLb6VfYmo93KQ54F+3oBO2qFRM/MRNBH912zd+5PboeE1ObjhM
 yoLPSrosmR3RH46Ahea2kl83
IronPort-SDR: e8UzC4EhYT2SsvX0FULuhr+9d/J6qVjAqENrkrGria3fTczrSYlVgjzEDmmxRYBDG4A3S+VCdd
 E59O3o2f2C2UFmZ+lemsvEK1bF4vgoA/vWul+ODnUJnEYrAGEGjDdZS4AdcekeWTH9592EshyT
 oDr2bJ4nBe/RptmtPzpiwQ9eKCUCqO0dfZsDzyCkSsek382vCehazSV2cxeQODTVxzi2Y4oNUU
 hAW7CzxGSetExATztsx+wQe8UrMCaWn5ii3fIztR0FIOvCIn4NYL3exAKV3zhTQVllakYMufkq
 4hc=
WDCIronportException: Internal
Message-ID: <9c479bb6-bb57-9b5a-2fa5-7b4d1b840245@opensource.wdc.com>
Date:   Wed, 24 Aug 2022 16:54:42 -0700
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0)
 Gecko/20100101 Thunderbird/91.12.0
Subject: Re: [PATCH] ATA: ACPI: Do not check ACPI_FADT_LOW_POWER_S0
Content-Language: en-US
To:     "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc:     linux-ide@vger.kernel.org, Linux ACPI <linux-acpi@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Mario Limonciello <mario.limonciello@amd.com>
References: <4426478.LvFx2qVVIh@kreacher>
From:   Damien Le Moal <damien.lemoal@opensource.wdc.com>
Organization: Western Digital Research
In-Reply-To: <4426478.LvFx2qVVIh@kreacher>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 2022/08/24 10:29, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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@intel.com>
> ---
>  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