ALSA: hda - Make single_cmd option to stop the fallback mechanism

HD-audio driver has a mechanism to fall back to the single cmd mode as
a last resort if the CORB/RIRB communication goes wrong even after
switching to the polling mode.  The switching has worked in the past
well, but Enrico Mioso reported that his system crashes when this
happens.

Although the actual cause of the crash isn't still fully analyzed yet,
it'd be in anyway good to provide an option to turn off the fallback
mode.  Now this patch extends the behavior of the existing single_cmd
option for that.  Namely,

- The option is changed from bool to bint.
- As default, it is the mode allowing the fallback to single cmd.
- Once when either true/false value is given to the option, the driver
  explicitly turns on/off the single cmd mode, but without the
  fallback.

That is, if you want to disable the fallback, just pass single_cmd=0
option.  Passing single_cmd=1 will keep working like before.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/hda_controller.c

@@ -861,6 +861,10 @@ static int azx_rirb_get_response(struct hdac_bus *bus, unsigned int addr,
 		return -EIO;
 	}
 
+	/* no fallback mechanism? */
+	if (!chip->fallback_to_single_cmd)
+		return -EIO;
+
 	/* a fatal communication error; need either to reset or to fallback
 	 * to the single_cmd mode
 	 */

sound/pci/hda/hda_controller.h

@@ -150,6 +150,7 @@ struct azx {
 	int bdl_pos_adj;
 	int poll_count;
 	unsigned int running:1;
+	unsigned int fallback_to_single_cmd:1;
 	unsigned int single_cmd:1;
 	unsigned int polling_mode:1;
 	unsigned int msi:1;

sound/pci/hda/hda_intel.c

@@ -128,7 +128,7 @@ static int bdl_pos_adj[SNDRV_CARDS] = {[0 ... (SNDRV_CARDS-1)] = -1};
 static int probe_mask[SNDRV_CARDS] = {[0 ... (SNDRV_CARDS-1)] = -1};
 static int probe_only[SNDRV_CARDS];
 static int jackpoll_ms[SNDRV_CARDS];
-static bool single_cmd;
+static int single_cmd = -1;
 static int enable_msi = -1;
 #ifdef CONFIG_SND_HDA_PATCH_LOADER
 static char *patch[SNDRV_CARDS];
@@ -157,7 +157,7 @@ module_param_array(probe_only, int, NULL, 0444);
 MODULE_PARM_DESC(probe_only, "Only probing and no codec initialization.");
 module_param_array(jackpoll_ms, int, NULL, 0444);
 MODULE_PARM_DESC(jackpoll_ms, "Ms between polling for jack events (default = 0, using unsol events only)");
-module_param(single_cmd, bool, 0444);
+module_param(single_cmd, bint, 0444);
 MODULE_PARM_DESC(single_cmd, "Use single command to communicate with codecs "
 		 "(for debugging only).");
 module_param(enable_msi, bint, 0444);
@@ -1596,7 +1596,11 @@ static int azx_create(struct snd_card *card, struct pci_dev *pci,
 
 	check_probe_mask(chip, dev);
 
-	chip->single_cmd = single_cmd;
+	if (single_cmd < 0) /* allow fallback to single_cmd at errors */
+		chip->fallback_to_single_cmd = 1;
+	else /* explicitly set to single_cmd or not */
+		chip->single_cmd = single_cmd;
+
 	azx_check_snoop_available(chip);
 
 	if (bdl_pos_adj[dev] < 0)