V4L/DVB (13327): em28xx: fix alt modprobe parameter

It seems that some patch broke alt modprobe parameter. Fix it to allow
changing alternate interfaces during module load and at runtime.

If changed during runtime, you'll need to stop a and restart stream for
the parameter to be used.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/em28xx/em28xx-core.c

@@ -50,7 +50,7 @@ MODULE_PARM_DESC(reg_debug, "enable debug messages [URB reg]");
 		printk(KERN_INFO "%s %s :"fmt, \
 			 dev->name, __func__ , ##arg); } while (0)
 
-static int alt = EM28XX_PINOUT;
+static int alt;
 module_param(alt, int, 0644);
 MODULE_PARM_DESC(alt, "alternate setting to use for video endpoint");
 
@@ -778,6 +778,16 @@ int em28xx_set_alternate(struct em28xx *dev)
 	int i;
 	unsigned int min_pkt_size = dev->width * 2 + 4;
 
+	/*
+	 * alt = 0 is used only for control messages, so, only values
+	 * greater than 0 can be used for streaming.
+	 */
+	if (alt && alt < dev->num_alt) {
+		em28xx_coredbg("alternate forced to %d\n", dev->alt);
+		dev->alt = alt;
+		goto set_alt;
+	}
+
 	/* When image size is bigger than a certain value,
 	   the frame size should be increased, otherwise, only
 	   green screen will be received.
@@ -798,6 +808,7 @@ int em28xx_set_alternate(struct em28xx *dev)
 			dev->alt = i;
 	}
 
+set_alt:
 	if (dev->alt != prev_alt) {
 		em28xx_coredbg("minimum isoc packet size: %u (alt=%d)\n",
 				min_pkt_size, dev->alt);

drivers/media/video/em28xx/em28xx.h

@@ -143,9 +143,6 @@
  */
 #define EM28XX_NUM_PACKETS 40
 
-/* default alternate; 0 means choose the best */
-#define EM28XX_PINOUT 0
-
 #define EM28XX_INTERLACED_DEFAULT 1
 
 /*