ALSA: support module on-demand loading for seq and timer

If CONFIG_SND_DYNAMIC_MINORS is used, assign /dev/snd/seq and
/dev/snd/timer the usual static minors, and export specific
module aliases to generate udev module on-demand loading
instructions:

$ cat /lib/modules/2.6.33.4-smp/modules.devname
# Device nodes to trigger on-demand module loading.
microcode cpu/microcode c10:184
fuse fuse c10:229
ppp_generic ppp c108:0
tun net/tun c10:200
uinput uinput c10:223
dm_mod mapper/control c10:236
snd_timer snd/timer c116:33
snd_seq snd/seq c116:1

The last two lines instruct udev to create device nodes, even
when the modules are not loaded at that time.

As soon as userspace accesses any of these nodes, the in-kernel
module-loader will load the module, and the device can be used.

The header file minor calculation needed to be simplified to
make __stringify() (supports only two indirections) in
the MODULE_ALIAS macro work.

This is part of systemd's effort to get rid of unconditional
module load instructions and needless init scripts.

Cc: Lennart Poettering <[e-mail]>
Signed-off-by: Kay Sievers <[e-mail]>
Signed-off-by: Clemens Ladisch <[e-mail]>
Signed-off-by: Takashi Iwai <[e-mail]>

include/sound/minors.h

···
 /* these minors can still be used for autoloading devices (/dev/aload*) */
 #define SNDRV_MINOR_CONTROL		0	/* 0 */
 #define SNDRV_MINOR_GLOBAL		1	/* 1 */
-#define SNDRV_MINOR_SEQUENCER		(SNDRV_MINOR_GLOBAL + 0 * 32)
-#define SNDRV_MINOR_TIMER		(SNDRV_MINOR_GLOBAL + 1 * 32)
+#define SNDRV_MINOR_SEQUENCER		1	/* SNDRV_MINOR_GLOBAL + 0 * 32 */
+#define SNDRV_MINOR_TIMER		33	/* SNDRV_MINOR_GLOBAL + 1 * 32 */
 
 #ifndef CONFIG_SND_DYNAMIC_MINORS
 						/* 2 - 3 (reserved) */

sound/core/seq/seq.c

···
 #include "seq_timer.h"
 #include "seq_system.h"
 #include "seq_info.h"
+#include <sound/minors.h>
 #include <sound/seq_device.h>
 
 #if defined(CONFIG_SND_SEQ_DUMMY_MODULE)
···
 MODULE_PARM_DESC(seq_default_timer_subdevice, "The default timer subdevice number.");
 module_param(seq_default_timer_resolution, int, 0644);
 MODULE_PARM_DESC(seq_default_timer_resolution, "The default timer resolution in Hz.");
+
+MODULE_ALIAS_CHARDEV(CONFIG_SND_MAJOR, SNDRV_MINOR_SEQUENCER);
+MODULE_ALIAS("devname:snd/seq");
 
 /*
  *  INIT PART

sound/core/sound.c

···
 };
 
 #ifdef CONFIG_SND_DYNAMIC_MINORS
-static int snd_find_free_minor(void)
+static int snd_find_free_minor(int type)
 {
 	int minor;
 
+	/* static minors for module auto loading */
+	if (type == SNDRV_DEVICE_TYPE_SEQUENCER)
+		return SNDRV_MINOR_SEQUENCER;
+	if (type == SNDRV_DEVICE_TYPE_TIMER)
+		return SNDRV_MINOR_TIMER;
+
 	for (minor = 0; minor < ARRAY_SIZE(snd_minors); ++minor) {
-		/* skip minors still used statically for autoloading devices */
-		if (SNDRV_MINOR_DEVICE(minor) == SNDRV_MINOR_CONTROL ||
-		    minor == SNDRV_MINOR_SEQUENCER)
+		/* skip static minors still used for module auto loading */
+		if (SNDRV_MINOR_DEVICE(minor) == SNDRV_MINOR_CONTROL)
+			continue;
+		if (minor == SNDRV_MINOR_SEQUENCER ||
+		    minor == SNDRV_MINOR_TIMER)
 			continue;
 		if (!snd_minors[minor])
 			return minor;
···
 	preg->private_data = private_data;
 	mutex_lock(&sound_mutex);
 #ifdef CONFIG_SND_DYNAMIC_MINORS
-	minor = snd_find_free_minor();
+	minor = snd_find_free_minor(type);
 #else
 	minor = snd_kernel_minor(type, card, dev);
 	if (minor >= 0 && snd_minors[minor])

sound/core/timer.c

···
 module_param(timer_tstamp_monotonic, int, 0444);
 MODULE_PARM_DESC(timer_tstamp_monotonic, "Use posix monotonic clock source for timestamps (default).");
 
+MODULE_ALIAS_CHARDEV(CONFIG_SND_MAJOR, SNDRV_MINOR_TIMER);
+MODULE_ALIAS("devname:snd/timer");
+
 struct snd_timer_user {
 	struct snd_timer_instance *timeri;
 	int tread;		/* enhanced read with timestamps and events */