ALSA: hdac: clear link output stream mapping

Fix potential DMA hang upon starting playback on devices in HDA mode
on Intel platforms (Gemini Lake/Whiskey Lake/Comet Lake/Ice Lake). It
doesn't affect platforms before Gemini Lake or any Intel device in
non-HDA mode.

The reset value for the LOSDIV register is all output streams valid.
Clear this register to invalidate non-existent streams when the bus
is powered up.

Signed-off-by: Rander Wang <rander.wang@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20190930142945.7805-1-pierre-louis.bossart@linux.intel.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/hda/ext/hdac_ext_controller.c

@@ -270,6 +270,11 @@ int snd_hdac_ext_bus_link_get(struct hdac_bus *bus,
 
 		ret = snd_hdac_ext_bus_link_power_up(link);
 
+		/*
+		 * clear the register to invalidate all the output streams
+		 */
+		snd_hdac_updatew(link->ml_addr, AZX_REG_ML_LOSIDV,
+				 ML_LOSIDV_STREAM_MASK, 0);
 		/*
 		 *  wait for 521usec for codec to report status
 		 *  HDA spec section 4.3 - Codec Discovery