linux-kernel - Re: [3.6-rc7] switcheroo race with Intel HDA...

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Message-ID: <s5hfw5ng5jw.wl%tiwai@suse.de>
Date:	Tue, 09 Oct 2012 15:04:35 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Daniel J Blueman <daniel@...ra.org>
Cc:	Dave Airlie <airlied@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	alsa-devel@...a-project.org
Subject: Re: [3.6-rc7] switcheroo race with Intel HDA...

At Tue, 9 Oct 2012 19:23:56 +0800,
Daniel J Blueman wrote:
> 
> On 9 October 2012 18:07, Takashi Iwai <tiwai@...e.de> wrote:
> > At Tue, 09 Oct 2012 12:04:08 +0200,
> > Takashi Iwai wrote:
> >>
> >> At Tue, 9 Oct 2012 00:34:09 +0800,
> >> Daniel J Blueman wrote:
> >> >
> >> > On 8 October 2012 20:58, Takashi Iwai <tiwai@...e.de> wrote:
> >> > > At Tue, 25 Sep 2012 13:20:05 +0800,
> >> > > Daniel J Blueman wrote:
> >> > >> On my Macbook with a discrete Nvidia GPU, there is a race between
> >> > >> selecting the integrated GPU and putting the discrete GPU into D3 [1],
> >> > >> reliably causing a kernel oops [2].
> >> > >>
> >> > >> Introducing a delay of ~1s between the calls prevents this. When the
> >> > >> second 'OFF' write path executes, it looks like struct azx at
> >> > >> card->private_data hasn't yet been allocated yet [3], so there is
> >> > >> likely some locking missing.
> >> > >
> >> > > It's rather pci_get_drvdata() returning NULL (i.e. card is NULL, thus
> >> > > card->private_data causes Oops).  Could you check the patch like below
> >> > > and see whether you get a kernel warning (but no Oops) or the problem
> >> > > gets fixed by shifting the assignment of pci drvdata?
> >> > [...]
> >> >
> >> > Good patching. Calling pci_set_drvdata later prevents the oops in HDA,
> >> > though we see unexpected 0x0 responses in the response ring buffer
> >> > [1], which we don't see when there's a >~1.5s delay between IGD and
> >> > OFF.
> >>
> >> If the previous patch fixed, it means that the switching occurred
> >> during the device was being probed.  Maybe a better approach to
> >> register the VGA switcheroo after the proper initialization.
> >>
> >> The patch below is a revised one.  Please give it a try.
> >
> > Also, it's not clear which card spews the spurious response.
> > Apply the patch below in addition.
> [...]
> 
> hda-intel: 0000:01:00.1: spurious response 0x0:0x0, last cmd=0x1f0004
> $ lspci -s :1:0.1
> 01:00.1 Audio device: NVIDIA Corporation Device 0e1b (rev ff)
> 
> It's the NVIDIA device which presumably hasn't completed it's
> transition to D3 at the time the OFF is executed.

OK, then could you try the patch below on the top of previous two
patches?


Takashi

---
diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
index f09ff6c..676c64d 100644
--- a/sound/pci/hda/hda_intel.c
+++ b/sound/pci/hda/hda_intel.c
@@ -2639,13 +2640,13 @@ static void azx_vs_set_state(struct pci_dev *pci,
 			   disabled ? "Disabling" : "Enabling",
 			   pci_name(chip->pci));
 		if (disabled) {
+			snd_hda_lock_devices(chip->bus);
 			azx_suspend(&pci->dev);
 			chip->disabled = true;
-			snd_hda_lock_devices(chip->bus);
 		} else {
-			snd_hda_unlock_devices(chip->bus);
 			chip->disabled = false;
 			azx_resume(&pci->dev);
+			snd_hda_unlock_devices(chip->bus);
 		}
 	}
 }
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