See kernel.org bugzilla page for description My HP Compaq 6715s is also affected, patch in attachment Reproducible: Always
Created attachment 170470 [details, diff] add HP Compaq 6715s laptop to blacklist
Patch included in gentoo-sources-2.6.27-r3 which is now in portage.
I've tested gentoo-sources-2.6.27-r4 and problem is the same. Adding this laptop model to the blacklist solves this problem
Created attachment 173340 [details, diff] SB600 fix Please revert the blacklist patch that you added to -r4, apply this one instead, and let us know if the problem remains
Done. The patch is OK. Thanks
fixed in gentoo-sources-2.6.27-r5