Re: [ 51/68] PCI: EHCI: fix crash during suspend on ASUS computers

[Herton Ronaldo Krzesinski]

On Thu, Jul 12, 2012 at 04:02:25PM -0700, Greg Kroah-Hartman wrote:
> From: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
> 
> 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 <stern@xxxxxxxxxxxxxxxxxxx>
> 
> 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.
> 
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Herton
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