[alsa-devel] HD-Audio: How to reduce driver initializaton time if multiple codecs present on the bus?

[Takashi Iwai]

At Mon, 02 Dec 2013 10:52:00 +0100,
Takashi Iwai wrote:
> 
> At Mon, 2 Dec 2013 09:48:24 +0000,
> Lin, Mengdong wrote:
> > 
> > > -----Original Message-----
> > > From: Takashi Iwai [mailto:tiwai at suse.de]
> > > Sent: Monday, December 02, 2013 4:24 PM
> > 
> > 
> > > > > > > > Btw, using a deferred azx_probe_continue (like we do if
> > > > > > > > there's a firmware file), would one get more parallelization with
> > > other drivers?
> > > > > > > > If so we could consider making that the default.
> > > > > > >
> > > > > > > This sounds like a good idea as we have already that code.  The
> > > > > > > patch would be just a few-liners.
> > > > > >
> > > > > > If azx_probe_continue() is delayed, could user space get
> > > > > > incomplete
> > > > > audio information after boot?
> > > > > > I mean is it possible that azx_probe_continue() does not complete
> > > > > before user space check ALSA info?
> > > > >
> > > > > Not impossible.  But then user-space should be triggered in event
> > > > > driven way by udev or such.
> > > >
> > > > Hi Takashi/David,
> > > >
> > > > So is it okay to defer azx_probe_continue() by default?
> > > 
> > > Yes.
> > > 
> > > > If yes, is it also necessary to defer snd_card_create() at the end of
> > > azx_probe_continue()?
> > > 
> > > No, that's a significant difference.  The snd_card_create() invocation isn't
> > > related with the hardware access itself, thus it's no point to delay.  If you
> > > delay the card instance creation, this may result in races between the card
> > > order, which we'd like to avoid.
> > > 
> > > > So user space can only see the sound card when azx_probe_continue()
> > > completes.
> > > 
> > > The completion of the card creation is notified only after
> > > snd_card_register(), so it doesn't matter when to call snd_card_create().
> > > 
> > > The below is an untested patch.  I should have added in the previous
> > > reply...
> > 
> > Hi Takashi,
> > 
> > Many thanks for the patch and information!
> > 
> > Is my understanding below is right?
> > snd_card_register() will create the device files under /sys/devices/pci0000:00/0000:00:1b.0/sound/cardx 
> > (or /sys/devices/pci0000:00/0000:00:03.0/sound/cardx for Haswell display audio), and trigger uevent to notify user space that an audio device is ready.
> > 
> > And for the patch, 
> 
> Yes.
> 
> > >  #ifdef CONFIG_SND_HDA_PATCH_LOADER
> > >  	if (patch[dev] && *patch[dev]) {
> > > @@ -3855,25 +3855,17 @@ static int azx_probe(struct pci_dev *pci,
> > >  					      azx_firmware_cb);
> > >  		if (err < 0)
> > >  			goto out_free;
> > > -		probe_now = false; /* continued in azx_firmware_cb() */
> > > +		schedule_probe = false; /* continued in azx_firmware_cb() */
> > >  	}
> > 
> > Should it be 'schedule_probe = true'?
> > I guess the driver intends to defer firmware loading.
> 
> No, in the case of f/w loading, f/w loader itself calls
> azx_probe_continue(), thus you don't need to schedule it manually.
> 
> We may move the f/w loading into azx_probe_continue() for simplicity,
> though, after applying the always-deferred-probe patch.  Then it can
> be back to request_firmware() again (not _nowait()).

BTW, while checking my previous patch, I noticed that the
complete_all() should be put in the delayed probe part, too.
The following patch fixes it.


Takashi

-- 8< --
From: Takashi Iwai <tiwai at suse.de>
Subject: [PATCH] ALSA: hda - Fix complete_all() timing in deferred probes

When the probe of snd-hda-intel driver is deferred due to f/w loading
or the nested module loading, complete_all() should be also delayed
until the initialization really finished.  Otherwise, vga-switcheroo
client would start switching before the actual init is done.

Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/pci/hda/hda_intel.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
index c6d230193da6..27aa14007cbd 100644
--- a/sound/pci/hda/hda_intel.c
+++ b/sound/pci/hda/hda_intel.c
@@ -3876,7 +3876,8 @@ static int azx_probe(struct pci_dev *pci,
 	}
 
 	dev++;
-	complete_all(&chip->probe_wait);
+	if (chip->disabled)
+		complete_all(&chip->probe_wait);
 	return 0;
 
 out_free:
@@ -3953,10 +3954,10 @@ static int azx_probe_continue(struct azx *chip)
 	if ((chip->driver_caps & AZX_DCAPS_PM_RUNTIME) || chip->use_vga_switcheroo)
 		pm_runtime_put_noidle(&pci->dev);
 
-	return 0;
-
 out_free:
-	chip->init_failed = 1;
+	if (err < 0)
+		chip->init_failed = 1;
+	complete_all(&chip->probe_wait);
 	return err;
 }
 
-- 
1.8.4.4