Re: switcheroo registration vs switching race...

[Takashi Iwai <tiwai@suse.de>]

At Wed, 28 Nov 2012 11:45:07 +0800,
Daniel J Blueman wrote:
> 
> Hi Seth, Dave, Takashi,
> 
> If I power down the unused discrete GPU before lightdm starts by
> fiddling with the sysfs file [1] in the upstart script, I see a race
> manifesting as the discrete GPU's HDA controller timing out to
> commands [2].
> 
> Adding some debug, I see that the registered audio devices are put
> into D3 before the GPU is, but it turns out that the discrete (and
> internal) GPU's HDA controller gets registered a bit later, so the
> list is empty. The symptom is since the HDA driver it's talking to
> hardware which is now in D3.
> 
> We could add a mutex to nouveau to allow us to wait for the DGPU HDA
> controller, but perhaps this should be solved at a higher level in the
> vgaswitcheroo code; what do you think?

Maybe it's a side effect for the recent effort to fix another race in
the probe.  A part of them problem is that the registration is done at
the very last of probing.

Instead of delaying the registration, how about the patch below?


Takashi

---
diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
index 4bb52da..17fbd68 100644
--- a/sound/pci/hda/hda_intel.c
+++ b/sound/pci/hda/hda_intel.c
@@ -49,6 +49,7 @@
 #include <linux/pm_runtime.h>
 #include <linux/clocksource.h>
 #include <linux/time.h>
+#include <linux/completion.h>
 
 #ifdef CONFIG_X86
 /* for snoop control */
@@ -469,6 +470,7 @@ struct azx {
 	/* locks */
 	spinlock_t reg_lock;
 	struct mutex open_mutex;
+	struct completion probe_wait;
 
 	/* streams (x num_streams) */
 	struct azx_dev *azx_dev;
@@ -2790,6 +2792,7 @@ static bool azx_vs_can_switch(struct pci_dev *pci)
 	struct snd_card *card = pci_get_drvdata(pci);
 	struct azx *chip = card->private_data;
 
+	wait_for_completion(&chip->probe_wait);
 	if (chip->init_failed)
 		return false;
 	if (chip->disabled || !chip->bus)
@@ -2851,6 +2854,9 @@ static int azx_free(struct azx *chip)
 
 	azx_notifier_unregister(chip);
 
+	chip->init_failed = 1; /* to be sure */
+	complete(&chip->probe_wait);
+
 	if (use_vga_switcheroo(chip)) {
 		if (chip->disabled && chip->bus)
 			snd_hda_unlock_devices(chip->bus);
@@ -3156,6 +3162,7 @@ static int __devinit azx_create(struct snd_card *card, struct pci_dev *pci,
 	INIT_LIST_HEAD(&chip->pcm_list);
 	INIT_LIST_HEAD(&chip->list);
 	init_vga_switcheroo(chip);
+	init_completion(&chip->probe_wait);
 
 	chip->position_fix[0] = chip->position_fix[1] =
 		check_position_fix(chip, position_fix[dev]);
@@ -3462,6 +3469,13 @@ static int __devinit azx_probe(struct pci_dev *pci,
 	}
 #endif /* CONFIG_SND_HDA_PATCH_LOADER */
 
+	err = register_vga_switcheroo(chip);
+	if (err < 0) {
+		snd_printk(KERN_ERR SFX
+			   "Error registering VGA-switcheroo client\n");
+		goto out_free;
+	}
+
 	if (probe_now) {
 		err = azx_probe_continue(chip);
 		if (err < 0)
@@ -3473,14 +3487,8 @@ static int __devinit azx_probe(struct pci_dev *pci,
 	if (pci_dev_run_wake(pci))
 		pm_runtime_put_noidle(&pci->dev);
 
-	err = register_vga_switcheroo(chip);
-	if (err < 0) {
-		snd_printk(KERN_ERR SFX
-			   "Error registering VGA-switcheroo client\n");
-		goto out_free;
-	}
-
 	dev++;
+	complete(&chip->probe_wait);
 	return 0;
 
 out_free: