On Thu, Jul 12, 2012 at 04:02:25PM -0700, Greg Kroah-Hartman wrote: > From: Greg KH <gre...@linuxfoundation.org> > > 3.0-stable review patch. If anyone has any objections, please let me know. > > ------------------
Missing also the diff/"signoff area" on this one. > > From: Alan Stern <st...@rowland.harvard.edu> > > commit dbf0e4c7257f8d684ec1a3c919853464293de66e upstream. > > Quite a few ASUS computers experience a nasty problem, related to the > EHCI controllers, when going into system suspend. It was observed > that the problem didn't occur if the controllers were not put into the > D3 power state before starting the suspend, and commit > 151b61284776be2d6f02d48c23c3625678960b97 (USB: EHCI: fix crash during > suspend on ASUS computers) was created to do this. > > It turned out this approach messed up other computers that didn't have > the problem -- it prevented USB wakeup from working. Consequently > commit c2fb8a3fa25513de8fedb38509b1f15a5bbee47b (USB: add > NO_D3_DURING_SLEEP flag and revert 151b61284776be2) was merged; it > reverted the earlier commit and added a whitelist of known good board > names. > > Now we know the actual cause of the problem. Thanks to AceLan Kao for > tracking it down. > > According to him, an engineer at ASUS explained that some of their > BIOSes contain a bug that was added in an attempt to work around a > problem in early versions of Windows. When the computer goes into S3 > suspend, the BIOS tries to verify that the EHCI controllers were first > quiesced by the OS. Nothing's wrong with this, but the BIOS does it > by checking that the PCI COMMAND registers contain 0 without checking > the controllers' power state. If the register isn't 0, the BIOS > assumes the controller needs to be quiesced and tries to do so. This > involves making various MMIO accesses to the controller, which don't > work very well if the controller is already in D3. The end result is > a system hang or memory corruption. > > Since the value in the PCI COMMAND register doesn't matter once the > controller has been suspended, and since the value will be restored > anyway when the controller is resumed, we can work around the BIOS bug > simply by setting the register to 0 during system suspend. This patch > (as1590) does so and also reverts the second commit mentioned above, > which is now unnecessary. > > In theory we could do this for every PCI device. However to avoid > introducing new problems, the patch restricts itself to EHCI host > controllers. > > Finally the affected systems can suspend with USB wakeup working > properly. > > -- > To unsubscribe from this list: send the line "unsubscribe stable" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- []'s Herton -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
