[alsa-devel] [PATCH v5] ALSA: usb: Work around CM6631 sample rate change bug

[Takashi Iwai]

At Wed, 03 Apr 2013 12:15:49 +0200,
Clemens Ladisch wrote:
> 
> Takashi Iwai wrote:
> > Torstein Hegge wrote:
> >> The C-Media CM6631 USB receiver doesn't respond to changes in sample rate
> >> while the interface is active. The same behavior is observed in other UAC2
> >> hardware like the VIA VT1731.
> >>
> >> Reset the interface after setting the sampling frequency on sample rate
> >> changes, to ensure that the sample rate set by snd_usb_init_sample_rate() is
> >> used. Otherwise, the device will try to use the sample rate of the previous
> >> stream, causing distorted sound on sample rate changes.
> >>
> >> The reset is performed for all UAC2 devices, as it should not affect a
> >> standards compliant device, but it is only necessary for C-Media CM6631,
> >> VIA VT1731 and possibly others.
> >>
> >> Failure to read sample rate from the device is not handled as an error in
> >> set_sample_rate_v2(), as (permanent or intermittent) failure to read sample
> >> rate isn't essential for a successful sample rate set.
> >>
> >> Signed-off-by: Torstein Hegge <hegge at resisty.net>
> >
> > What about the latest status of the patch?
> >
> > If both Clemens and Daniel are happy with it, I can apply it for the
> > next 3.9-rc.
> 
> Acked-by: Clemens Ladisch <clemens at ladisch.de>
> with or without this change:

OK, I applied the patch now without modification for for-linus
branch.  Then back-merged to for-next branch with the additional
clean-up patch below.

Eldad, please rebase your patches to for-next branch of sound git
tree.


thanks,

Takashi

---
From: Takashi Iwai <tiwai at suse.de>
Subject: [PATCH] ALSA: usb-audio: Clean up the code in set_sample_rate_v2()

Just for cleaning up, introduce a new function get_sample_rate_v2()
for replacing two identical calls in set_sample_rate_v2().

No functional change.

Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/usb/clock.c | 47 +++++++++++++++++++++++------------------------
 1 file changed, 23 insertions(+), 24 deletions(-)

diff --git a/sound/usb/clock.c b/sound/usb/clock.c
index 9e2703a..e3ccf3d 100644
--- a/sound/usb/clock.c
+++ b/sound/usb/clock.c
@@ -247,6 +247,27 @@ static int set_sample_rate_v1(struct snd_usb_audio *chip, int iface,
 	return 0;
 }
 
+static int get_sample_rate_v2(struct snd_usb_audio *chip, int iface,
+			      int altsetting, int clock)
+{
+	struct usb_device *dev = chip->dev;
+	unsigned char data[4];
+	int err;
+
+	err = snd_usb_ctl_msg(dev, usb_rcvctrlpipe(dev, 0), UAC2_CS_CUR,
+			      USB_TYPE_CLASS | USB_RECIP_INTERFACE | USB_DIR_IN,
+			      UAC2_CS_CONTROL_SAM_FREQ << 8,
+			      snd_usb_ctrl_intf(chip) | (clock << 8),
+			      data, sizeof(data));
+	if (err < 0) {
+		snd_printk(KERN_WARNING "%d:%d:%d: cannot get freq (v2)\n",
+			   dev->devnum, iface, altsetting);
+		return 0;
+	}
+
+	return data[0] | (data[1] << 8) | (data[2] << 16) | (data[3] << 24);
+}
+
 static int set_sample_rate_v2(struct snd_usb_audio *chip, int iface,
 			      struct usb_host_interface *alts,
 			      struct audioformat *fmt, int rate)
@@ -266,18 +287,7 @@ static int set_sample_rate_v2(struct snd_usb_audio *chip, int iface,
 		return -ENXIO;
 	}
 
-	err = snd_usb_ctl_msg(dev, usb_rcvctrlpipe(dev, 0), UAC2_CS_CUR,
-			      USB_TYPE_CLASS | USB_RECIP_INTERFACE | USB_DIR_IN,
-			      UAC2_CS_CONTROL_SAM_FREQ << 8,
-			      snd_usb_ctrl_intf(chip) | (clock << 8),
-			      data, sizeof(data));
-	if (err < 0) {
-		snd_printk(KERN_WARNING "%d:%d:%d: cannot get freq (v2)\n",
-			   dev->devnum, iface, fmt->altsetting);
-		prev_rate = 0;
-	} else {
-		prev_rate = data[0] | (data[1] << 8) | (data[2] << 16) | (data[3] << 24);
-	}
+	prev_rate = get_sample_rate_v2(chip, iface, fmt->altsetting, clock);
 
 	data[0] = rate;
 	data[1] = rate >> 8;
@@ -293,18 +303,7 @@ static int set_sample_rate_v2(struct snd_usb_audio *chip, int iface,
 		return err;
 	}
 
-	err = snd_usb_ctl_msg(dev, usb_rcvctrlpipe(dev, 0), UAC2_CS_CUR,
-			      USB_TYPE_CLASS | USB_RECIP_INTERFACE | USB_DIR_IN,
-			      UAC2_CS_CONTROL_SAM_FREQ << 8,
-			      snd_usb_ctrl_intf(chip) | (clock << 8),
-			      data, sizeof(data));
-	if (err < 0) {
-		snd_printk(KERN_WARNING "%d:%d:%d: cannot get freq (v2)\n",
-			   dev->devnum, iface, fmt->altsetting);
-		cur_rate = 0;
-	} else {
-		cur_rate = data[0] | (data[1] << 8) | (data[2] << 16) | (data[3] << 24);
-	}
+	cur_rate = get_sample_rate_v2(chip, iface, fmt->altsetting, clock);
 
 	if (cur_rate != rate) {
 		snd_printd(KERN_WARNING
-- 
1.8.1.4