2 files changed, 56 insertions, 1 deletions

diff --git a/Documentation/sound/alsa/ALSA-Configuration.txt b/Documentation/sound/alsa/ALSA-Configuration.txt
index 8e49c19f6c96..f34821d6d52a 100644
--- a/Documentation/sound/alsa/ALSA-Configuration.txt
+++ b/Documentation/sound/alsa/ALSA-Configuration.txt
@@ -57,7 +57,9 @@ Prior to version 0.9.0rc4 options had a 'snd_' prefix. This was removed.
                 - Default: 1
                 - For auto-loading more than one card, specify this
                   option together with snd-card-X aliases.
-
+    slots       - Reserve the slot index for the given driver.
+                  This option takes multiple strings.           
+                  See "Module Autoloading Support" section for details.
   
   Module snd-pcm-oss
   ------------------
@@ -2140,6 +2142,23 @@ alias sound-slot-1 snd-ens1371
 In this example, the interwave card is always loaded as the first card
 (index 0) and ens1371 as the second (index 1).
 
+Alternative (and new) way to fixate the slot assignment is to use
+"slots" option of snd module.  In the case above, specify like the
+following: 
+
+options snd slots=snd-interwave,snd-ens1371
+
+Then, the first slot (#0) is reserved for snd-interwave driver, and
+the second (#1) for snd-ens1371.  You can omit index option in each
+driver if slots option is used (although you can still have them at
+the same time as long as they don't conflict).
+
+The slots option is especially useful for avoiding the possible
+hot-plugging and the resultant slot conflict.  For example, in the
+case above again, the first two slots are already reserved.  If any
+other driver (e.g. snd-usb-audio) is loaded before snd-interwave or
+snd-ens1371, it will be assigned to the third or later slot.
+
 
 ALSA PCM devices to OSS devices mapping
 =======================================
diff --git a/sound/core/init.c b/sound/core/init.c
index 2cb7099eb1e1..48d38a79cbbb 100644
--- a/sound/core/init.c
+++ b/sound/core/init.c
@@ -43,6 +43,40 @@ EXPORT_SYMBOL(snd_cards);
 
 static DEFINE_MUTEX(snd_card_mutex);
 
+static char *slots[SNDRV_CARDS];
+module_param_array(slots, charp, NULL, 0444);
+MODULE_PARM_DESC(slots, "Module names assigned to the slots.");
+
+/* return non-zero if the given index is already reserved for another
+ * module via slots option
+ */
+static int module_slot_mismatch(struct module *module, int idx)
+{
+#ifdef MODULE
+        char *s1, *s2;
+        if (!module || !module->name || !slots[idx])
+                return 0;
+        s1 = slots[idx];
+        s2 = module->name;
+        /* compare module name strings
+         * hyphens are handled as equivalent with underscore
+         */
+        for (;;) {
+                char c1 = *s1++;
+                char c2 = *s2++;
+                if (c1 == '-')
+                        c1 = '_';
+                if (c2 == '-')
+                        c2 = '_';
+                if (c1 != c2)
+                        return 1;
+                if (!c1)
+                        break;
+        }
+#endif
+        return 0;
+}
+
 #if defined(CONFIG_SND_MIXER_OSS) || defined(CONFIG_SND_MIXER_OSS_MODULE)
 int (*snd_mixer_oss_notify_callback)(struct snd_card *card, int free_flag);
 EXPORT_SYMBOL(snd_mixer_oss_notify_callback);
@@ -115,6 +149,8 @@ struct snd_card *snd_card_new(int idx, const char *xid,
                 for (idx2 = 0; idx2 < SNDRV_CARDS; idx2++)
                         /* idx == -1 == 0xffff means: take any free slot */
                         if (~snd_cards_lock & idx & 1<<idx2) {
+                                if (module_slot_mismatch(module, idx2))
+                                        continue;
                                 idx = idx2;
                                 if (idx >= snd_ecards_limit)
                                         snd_ecards_limit = idx + 1;