[alsa-devel] my udev rules are breaking my dmixer setup why?

[Takashi Iwai]

At Sun, 09 Nov 2008 15:59:03 +0100,
Jelle de Jong wrote:
> 
> Hello everybody,
> 
> I am trying to use udev to get fixed device names depending on the
> location of the device on the usb bus. The udev rules seems to be
> working fine, however i cant get dmix to work with the udev rules using
> only hw dies work. If i remove the udev rules the dmixer works fine.
> 
> Can somebody look at the attachment, and maybe do some testing, i would
> highly appreciate it.

Swapping the card numbers with udev might have a problem because
the driver itself remembers the card index, and this number isn't
swapped -- thus you get inconsistency between the device file and
the internal index number.

BTW, if you just would like to keep the fixed device index for a
certain usb device path, try my old patch below.
It adds devpath option to snd-usb-audio, and you can specify the
usb device path string ("usb-$BUSNAME-$DEVPATH").


Takashi

---
diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index bbd70d5..4e6ae0e 100644
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -68,6 +68,7 @@ static int enable[SNDRV_CARDS] = SNDRV_DEFAULT_ENABLE_PNP;/* Enable this card */
 /* Vendor/product IDs for this card */
 static int vid[SNDRV_CARDS] = { [0 ... (SNDRV_CARDS-1)] = -1 };
 static int pid[SNDRV_CARDS] = { [0 ... (SNDRV_CARDS-1)] = -1 };
+static char *devpath[SNDRV_CARDS];
 static int nrpacks = 8;		/* max. number of packets per urb */
 static int async_unlink = 1;
 static int device_setup[SNDRV_CARDS]; /* device parameter for this card*/
@@ -83,6 +84,8 @@ module_param_array(vid, int, NULL, 0444);
 MODULE_PARM_DESC(vid, "Vendor ID for the USB audio device.");
 module_param_array(pid, int, NULL, 0444);
 MODULE_PARM_DESC(pid, "Product ID for the USB audio device.");
+module_param_array(devpath, charp, NULL, 0444);
+MODULE_PARM_DESC(devpath, "USB devpath for the specific index.");
 module_param(nrpacks, int, 0644);
 MODULE_PARM_DESC(nrpacks, "Max. number of packets per URB.");
 module_param(async_unlink, bool, 0444);
@@ -3543,6 +3546,21 @@ static int snd_usb_audio_create(struct usb_device *dev, int idx,
 }
 
 
+static int is_matching_device(int i, u32 id, struct usb_device *dev)
+{
+	if (vid[i] != -1 && vid[i] != USB_ID_VENDOR(id))
+		return 0;
+	if (pid[i] != -1 && pid[i] != USB_ID_PRODUCT(id))
+		return 0;
+	if (devpath[i]) {
+		char tmppath[64];
+		usb_make_path(dev, tmppath, sizeof(tmppath));
+		if (strcmp(devpath[i], tmppath))
+			return 0;
+	}
+	return 1;
+}
+
 /*
  * probe the active usb device
  *
@@ -3613,8 +3631,7 @@ static void *snd_usb_audio_probe(struct usb_device *dev,
 		 */
 		for (i = 0; i < SNDRV_CARDS; i++)
 			if (enable[i] && ! usb_chip[i] &&
-			    (vid[i] == -1 || vid[i] == USB_ID_VENDOR(id)) &&
-			    (pid[i] == -1 || pid[i] == USB_ID_PRODUCT(id))) {
+			    is_matching_device(i, id, dev)) {
 				if (snd_usb_audio_create(dev, i, quirk, &chip) < 0) {
 					goto __error;
 				}