linux-kernel - Re: [RFC 2/2] ata: ahci: Protect users from setting policies their drives don't support

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Date:   Fri, 25 Feb 2022 22:20:12 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Mario Limonciello <mario.limonciello@....com>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>
Cc:     "open list:LIBATA SUBSYSTEM (Serial and Parallel ATA drivers)" 
        <linux-ide@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 2/2] ata: ahci: Protect users from setting policies their
 drives don't support

Hi,

On 2/25/22 19:10, Mario Limonciello wrote:
> As the default low power policy applies to more chipsets and drives, it's
> important to make sure that drives actually support the policy that a user
> selected in their kernel configuration.
> 
> If the drive doesn't support slumber, don't let the default policy for the
> ATA port be `min_power` or `min_power_with_partial`.
> 
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
>  drivers/ata/ahci.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
> index 17d757ad7111..af8999453084 100644
> --- a/drivers/ata/ahci.c
> +++ b/drivers/ata/ahci.c
> @@ -1584,8 +1584,16 @@ static int ahci_init_msi(struct pci_dev *pdev, unsigned int n_ports,
>  static void ahci_update_initial_lpm_policy(struct ata_port *ap,
>  					   struct ahci_host_priv *hpriv)
>  {
> +	struct pci_dev *pdev = to_pci_dev(ap->host->dev);
>  	int policy = CONFIG_SATA_LPM_POLICY;
>  
> +	if (policy >= ATA_LPM_MIN_POWER_WITH_PARTIAL &&
> +	   !(hpriv->cap & HOST_CAP_SSC)) {
> +		dev_warn(&pdev->dev,
> +			 "This drive doesn't support slumber; ignoring default SATA policy\n");
> +		return;
> +	}
> +

Don't the capabilties get checked later when the policy gets applied ?

At least I think they do get checked later, but I have not looked
at this code for years  ...  ?

Regards,

Hans


>  	/* user modified policy via module param */
>  	if (mobile_lpm_policy != -1) {
>  		policy = mobile_lpm_policy;