On Thu, 21 Jun 2007 15:08:32 +0200
Jens Axboe <jens.axboe@xxxxxxxxxx> wrote:
> On Wed, Jun 20 2007, Kristen Carlson Accardi wrote:
> > Enable Aggressive Link Power management for AHCI controllers.
> >
> > This patch will set the correct bits to turn on Aggressive
> > Link Power Management (ALPM) for the ahci driver. This
> > will cause the controller and disk to negotiate a lower
> > power state for the link when there is no activity (see
> > the AHCI 1.x spec for details). This feature is mutually
> > exclusive with Hot Plug, so when ALPM is enabled, Hot Plug
> > is disabled. ALPM will be enabled by default, but it is
> > settable via the scsi host syfs interface. Possible
> > settings for this feature are:
> >
> > Setting Effect
> > ----------------------------------------------------------
> > min_power ALPM is enabled, and link set to enter
> > lowest power state (SLUMBER) when idle
> > Hot plug not allowed.
> >
> > max_performance ALPM is disabled, Hot Plug is allowed
> >
> > medium_power ALPM is enabled, and link set to enter
> > second lowest power state (PARTIAL) when
> > idle. Hot plug not allowed.
> >
> > Signed-off-by: Kristen Carlson Accardi <kristen.c.accardi@xxxxxxxxx>
>
> A suggestion (it comes with a patch!) - default to max_power/almp off,
> not min_power. For two reasons:
>
> - There's such a big performance difference between the two, you really
> want max_power when booting.
>
> - It's a lot better to default to no change, than default to enabling
> something new.
Sounds reasonable to me. Distros/users can decide if they want to have
scripts that enable this after boot to run at min_power.
Acked-by: Kristen Carlson Accardi <kristen.c.accardi@xxxxxxxxx>
>
> diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
> index 841cf0a..e7a2072 100644
> --- a/drivers/ata/ahci.c
> +++ b/drivers/ata/ahci.c
> @@ -786,8 +786,7 @@ static int ahci_disable_alpm(struct ata_port *ap)
> return 0;
> }
>
> -static int ahci_enable_alpm(struct ata_port *ap,
> - enum scsi_host_link_pm policy)
> +static int ahci_enable_alpm(struct ata_port *ap, enum scsi_host_link_pm policy)
> {
> struct ahci_host_priv *hpriv = ap->host->private_data;
> void __iomem *port_mmio = ahci_port_base(ap);
> @@ -808,19 +807,19 @@ static int ahci_enable_alpm(struct ata_port *ap,
> return -EINVAL;
> }
>
> - switch(policy) {
> + switch (policy) {
> case SHOST_MAX_PERFORMANCE:
> - ahci_disable_alpm(ap);
> - ap->pm_policy = policy;
> - return 0;
> case SHOST_NOT_AVAILABLE:
> - case SHOST_MIN_POWER:
> /*
> * if we came here with SHOST_NOT_AVAILABLE,
> * it just means this is the first time we
> - * have tried to enable - so try to do
> - * min_power
> + * have tried to enable - default to max performance,
> + * and let the user go to lower power modes on request.
> */
> + ahci_disable_alpm(ap);
> + ap->pm_policy = SHOST_MAX_PERFORMANCE;
> + return 0;
> + case SHOST_MIN_POWER:
> ap->pm_policy = SHOST_MIN_POWER;
>
> /* configure HBA to enter SLUMBER */
>
> --
> Jens Axboe
>
-
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