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.
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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