ALSA: hda - Force to link down at runtime suspend on ATI/AMD HDMI

Henning Kühn reported that the discrete AMD GPU on his hybrid graphics
laptop no longer runtime-suspends due to the recent commit
07f4f97d ("vga_switcheroo: Use device link for HDA controller").

The root cause is that the HDMI codec on AMD GPU doesn't support
CLKSTOP and EPSS, which are currently mandatory for powering down the
HD-audio link at runtime suspend.  Because the HD-audio link is still
up, HD-audio controller driver blocks the transition to D3.

For addressing the regression, this patch adds a new flag to indicate
the forced link-down, and sets it for AMD HDMI codecs appropriately
in the codec driver.

Fixes: 07f4f97d ("vga_switcheroo: Use device link for HDA controller")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106957Reported-by: Lukas Wunner <lukas@wunner.de>
Reported-and-tested-by: Henning Kühn <prg@cooco.de>
Cc: <stable@vger.kernel.org> # v4.17+
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/hda_codec.c

@@ -2899,8 +2899,9 @@ static int hda_codec_runtime_suspend(struct device *dev)
 	list_for_each_entry(pcm, &codec->pcm_list_head, list)
 		snd_pcm_suspend_all(pcm->pcm);
 	state = hda_call_codec_suspend(codec);
-	if (codec_has_clkstop(codec) && codec_has_epss(codec) &&
-	    (state & AC_PWRST_CLK_STOP_OK))
+	if (codec->link_down_at_suspend ||
+	    (codec_has_clkstop(codec) && codec_has_epss(codec) &&
+	     (state & AC_PWRST_CLK_STOP_OK)))
 		snd_hdac_codec_link_down(&codec->core);
 	snd_hdac_link_power(&codec->core, false);
 	return 0;

sound/pci/hda/hda_codec.h

@@ -258,6 +258,7 @@ struct hda_codec {
 	unsigned int power_save_node:1; /* advanced PM for each widget */
 	unsigned int auto_runtime_pm:1; /* enable automatic codec runtime pm */
 	unsigned int force_pin_prefix:1; /* Add location prefix */
+	unsigned int link_down_at_suspend:1; /* link down at runtime suspend */
 #ifdef CONFIG_PM
 	unsigned long power_on_acct;
 	unsigned long power_off_acct;

sound/pci/hda/patch_hdmi.c

@@ -3741,6 +3741,11 @@ static int patch_atihdmi(struct hda_codec *codec)
 
 	spec->chmap.channels_max = max(spec->chmap.channels_max, 8u);
 
+	/* AMD GPUs have neither EPSS nor CLKSTOP bits, hence preventing
+	 * the link-down as is.  Tell the core to allow it.
+	 */
+	codec->link_down_at_suspend = 1;
+
 	return 0;
 }