ALSA: hda: do not override bus codec_mask in link_get()

snd_hdac_ext_bus_link_get() does not work correctly in case
there are multiple codecs on the bus. It unconditionally
resets the bus->codec_mask value. As per documentation in
hdaudio.h and existing use in client code, this field should
be used to store bit flag of detected codecs on the bus.

By overwriting value of the codec_mask, information on all
detected codecs is lost. No current user of hdac is impacted,
but use of bus->codec_mask is planned in future patches
for SOF.
Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20200206200223.7715-1-kai.vehmanen@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/hda/ext/hdac_ext_controller.c

@@ -254,6 +254,7 @@ EXPORT_SYMBOL_GPL(snd_hdac_ext_bus_link_power_down_all);
 int snd_hdac_ext_bus_link_get(struct hdac_bus *bus,
 				struct hdac_ext_link *link)
 {
+	unsigned long codec_mask;
 	int ret = 0;
 
 	mutex_lock(&bus->lock);
@@ -280,9 +281,11 @@ int snd_hdac_ext_bus_link_get(struct hdac_bus *bus,
 		 *  HDA spec section 4.3 - Codec Discovery
 		 */
 		udelay(521);
-		bus->codec_mask = snd_hdac_chip_readw(bus, STATESTS);
-		dev_dbg(bus->dev, "codec_mask = 0x%lx\n", bus->codec_mask);
-		snd_hdac_chip_writew(bus, STATESTS, bus->codec_mask);
+		codec_mask = snd_hdac_chip_readw(bus, STATESTS);
+		dev_dbg(bus->dev, "codec_mask = 0x%lx\n", codec_mask);
+		snd_hdac_chip_writew(bus, STATESTS, codec_mask);
+		if (!bus->codec_mask)
+			bus->codec_mask = codec_mask;
 	}
 
 	mutex_unlock(&bus->lock);