Re: [PATCH 2/2] em28xx: fix check for audio only usb interfaces when changing the usb alternate setting

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On 12.01.2014 18:37, Mauro Carvalho Chehab wrote:
Em Sat, 11 Jan 2014 14:42:30 +0100
Frank Schäfer <fschaefer.oss@xxxxxxxxxxxxxx> escreveu:

Previously, we've been assuming that the video endpoints are always at usb
interface 0. Hence, if vendor audio endpoints are provided at a separate
interface, they were supposed to be at interface number > 0.
Instead of checking for (interface number > 0) to determine if an interface is a
pure audio interface, dev->is_audio_only should be checked.

Signed-off-by: Frank Schäfer <fschaefer.oss@xxxxxxxxxxxxxx>
---
  drivers/media/usb/em28xx/em28xx-audio.c |   15 +++++++++++++--
  1 Datei geändert, 13 Zeilen hinzugefügt(+), 2 Zeilen entfernt(-)

diff --git a/drivers/media/usb/em28xx/em28xx-audio.c b/drivers/media/usb/em28xx/em28xx-audio.c
index b2ae954..18b745f 100644
--- a/drivers/media/usb/em28xx/em28xx-audio.c
+++ b/drivers/media/usb/em28xx/em28xx-audio.c
@@ -243,11 +243,22 @@ static int snd_em28xx_capture_open(struct snd_pcm_substream *substream)
  	}
runtime->hw = snd_em28xx_hw_capture;
-	if ((dev->alt == 0 || dev->ifnum) && dev->adev.users == 0) {
-		if (dev->ifnum)
+	if (dev->adev.users == 0 && (dev->alt == 0 || dev->is_audio_only)) {
+		if (dev->is_audio_only)
+			/* vendor audio is on a separate interface */
  			dev->alt = 1;
  		else
+			/* vendor audio is on the same interface as video */
  			dev->alt = 7;
+			/*
+			 * FIXME: The intention seems to be to select the alt
+			 * setting with the largest wMaxPacketSize for the video
+			 * endpoint.
+			 * At least dev->alt and dev->dvb_alt_isoc should be
+			 * used instead, but we should probably not touch it at
+			 * all if it is already >0, because wMaxPacketSize of
+			 * the audio endpoints seems to be the same for all.
+			 */
Actually, it should take into account only the analog case, since, in
digital mode, the audio comes via the MPEG stream instead.
Yes, of course you are absolutely right.
I will fix the comment.


Ok, it makes sense to return -EBUSY if one tries to use it while using
DVB.

dprintk("changing alternate number on interface %d to %d\n",
  			dev->ifnum, dev->alt);


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