On Fri, 4 Mar 2011 19:38:36 +0100
Tejun Heo <tj@xxxxxxxxxx> wrote:
> Hello,
>
> On Fri, Mar 04, 2011 at 10:24:11AM -0800, Kristen Carlson Accardi wrote:
> > case ATA_LPM_MIN_POWER:
> > - /* no restrictions on LPM transitions */
> > - scontrol &= ~(0x3 << 8);
> > + if (ata_link_nr_enabled(link) > 0)
> > + /* no restrictions on LPM transitions */
> > + scontrol &= ~(0x3 << 8);
> > + else {
> > + /* empty port, power off */
> > + scontrol &= ~0xf;
> > + scontrol |= (0x1 << 2);
> > + }
>
> Why not just do the following?
>
> scontrol &= ~(0x3 << 8);
because, the IPM value is meaningless if we have no devices,
so this is a wasted operation.
> /* if empty, power off */
> if (!ata_link_nr_enabled(link)) {
> scontrol &= ~0xf;
> scontrol |= 0x1 << 2;
> }
>
> Also, can you please provide some details on on which hardware you
> tested the change and how much power it actually saved?
>
This change was tested on Intel's Sandy Bridge platform. Your power
savings will depend on how many implemented ports you have, and how
many are not being used. For a system I tested with which had 2 ports
which I could turn off, I saved 300mW.
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