[ALSA] Add description about probe_mask option for snd-hda-intel

Added a brief description about probe_mask option for snd-hda-intel.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>

Documentation/sound/alsa/ALSA-Configuration.txt

@@ -759,6 +759,7 @@ Prior to version 0.9.0rc4 options had a 'snd_' prefix. This was removed.
 
     model	- force the model name
     position_fix - Fix DMA pointer (0 = auto, 1 = none, 2 = POSBUF, 3 = FIFO size)
+    probe_mask  - Bitmask to probe codecs (default = -1, meaning all slots)
     single_cmd  - Use single immediate commands to communicate with
 		codecs (for debugging only)
     enable_msi	- Enable Message Signaled Interrupt (MSI) (default = off)
@@ -966,6 +967,17 @@ Prior to version 0.9.0rc4 options had a 'snd_' prefix. This was removed.
     from the irq.  Remember this is a last resort, and should be
     avoided as much as possible...
     
+    MORE NOTES ON "azx_get_response timeout" PROBLEMS:
+    On some hardwares, you may need to add a proper probe_mask option
+    to avoid the "azx_get_response timeout" problem above, instead.
+    This occurs when the access to non-existing or non-working codec slot
+    (likely a modem one) causes a stall of the communication via HD-audio
+    bus.  You can see which codec slots are probed by enabling
+    CONFIG_SND_DEBUG_DETECT, or simply from the file name of the codec
+    proc files.  Then limit the slots to probe by probe_mask option.
+    For example, probe_mask=1 means to probe only the first slot, and
+    probe_mask=4 means only the third slot.
+
     The power-management is supported.
 
   Module snd-hdsp