I tried this patch and it doesn't work on ICH8 because it violates AHCI
protocol.
kristen.c.accardi@xxxxxxxxx wrote:
> --- linux-ahci-phy.orig/drivers/ata/libata-core.c 2008-06-27 13:32:51.000000000 -0700
> +++ linux-ahci-phy/drivers/ata/libata-core.c 2008-07-01 16:33:00.000000000 -0700
> @@ -162,6 +162,19 @@ MODULE_DESCRIPTION("Library module for A
> MODULE_LICENSE("GPL");
> MODULE_VERSION(DRV_VERSION);
>
> +static void ata_phy_offline(struct ata_link *link)
> +{
> + u32 scontrol;
> + int rc;
> +
> + /* set DET to 4 */
> + rc = sata_scr_read(link, SCR_CONTROL, &scontrol);
> + if (rc)
> + return;
> + scontrol &= ~0xf;
> + scontrol |= (1 << 2);
> + sata_scr_write(link, SCR_CONTROL, scontrol);
> +}
On AHCI, you can't change SCTL.DET when the port is running. This
version of ata_phy_offline changes SCTL.DET without regard to CMD.ST.
I would propose something more like this:
static void ata_port_offline(struct ata_port *ap)
{
u32 scontrol;
int rc;
struct ata_link *link = &ap->link;
if (ap->ops->port_stop)
ap->ops->port_stop(ap);
rc = sata_scr_read(link, SCR_CONTROL, &scontrol);
if (rc)
return;
scontrol &= ~0xf;
scontrol |= (1<<2);
sata_scr_write(link, SCR_CONTROL, scontrol);
}
I tried the above on ICH8 and by poking around in /dev/mem I believe it
works. After I set the ALPM to power_off in sysfs, the port shows
CMD.ST == 0, CMD.FRE == 0, and SSTS.DET == 4. So I think this is the
way to go, at least with respect to AHCI. I can't say whether this
makes sense generally for the other users of libata-core.
The problem is I didn't save any power this way :( ThinkPad X61t was
using minimum 7.6W on a one-minute average before power_off, and same
power after power_off. I'd been led to believe that disabling these
ports would have a substantial power saving effect.
-jwb
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