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

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Message-ID: <BL1PR12MB5157C0A33DC4484B6E5E6E91E23E9@BL1PR12MB5157.namprd12.prod.outlook.com>
Date:   Fri, 25 Feb 2022 21:24:17 +0000
From:   "Limonciello, Mario" <Mario.Limonciello@....com>
To:     Hans de Goede <hdegoede@...hat.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

[AMD Official Use Only]



> -----Original Message-----
> From: Hans de Goede <hdegoede@...hat.com>
> Sent: Friday, February 25, 2022 15:20
> To: Limonciello, Mario <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  ...  ?

There's a bunch of layers of indirection so I might have missed something,
but I didn't see anything in sata_link_scr_lpm or anywhere else for that
matter that actually checked HOST_CAP_SSC.

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