[PATCH] AHCI powersaving and port-stopping (2.6.22-rc4)

[John Fremlin]

Tejun Heo has made an excellent patch for saving power with the AHCI
chipset. It saves about 1 W on my Thinkpad X60s.

This patch will stop the ports when they are idle. To turn it on, 

     echo 1 > /sys/module/libata/parameters/powersave

This is very different from the patch I posted a while ago turning on
a few bits in the CMD register (ALPE and ASP) and which Intel is
apparently now trying. That only saves around 250mW. Tejun's patch
saves about 1 W. It should also make the ALPE and ASP stuff irrelevant
because it performs the same operation in software where better
information about usage is (theoretically) available.

I have updated the patch for 2.6.22-rc4. That is the extent of my
involvement - if it works, thank Tejun Heo. But problems are quite
likely to have been introduced by my clumsy update, so if it doesn't
work, blame me first.

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