Re: [PATCH] drm/i915: Acquire audio powerwell for HD-Audio registers

[Takashi Iwai <tiwai@suse.de>]

[dropped stable ML and add a few other relevant people to Cc]

On Thu, 04 Aug 2016 20:05:27 +0200,
Takashi Iwai wrote:
> 
> On Thu, 04 Aug 2016 18:44:11 +0200,
> Daniel Vetter wrote:
> > 
> > On Wed, Aug 03, 2016 at 05:09:00PM +0100, Chris Wilson wrote:
> > > On Haswell/Broadwell, the HD-Audio block is inside the HDMI/display
> > > power well and so the sna-hda audio codec acquires the display power
> > > well while it is operational. However, Skylake separates the powerwells
> > > again, but yet we still need the audio powerwell to setup the registers.
> > > (But then the hardware uses those registers even while powered off???)
> > 
> > Yeah feels fishy, but will at least duct-tape over the breakage from the
> > audio side. Most likely the reg writes go exactly nowhere and there's a
> > bug on the audio side. And this patch doesn't fix that.
> 
> Well, if the relevant code paths are only over these callbacks, I
> guess the following fix would work instead.
> 
> Can anyone check?

Scratch the previous one.  There is another place calling similarly.

Now looking back at the code again, I believe that the better way
would be to properly do power up / down at the resume callbacks.

Below is an untested patch.  Let me know if this actually works.


thanks,

Takashi

-- 8< --
From: Takashi Iwai <tiwai@suse.de>
Subject: [PATCH] ALSA: hda - Manage power well properly for resume

For SKL and later Intel chips, we control the power well per codec
basis via link_power callback since the commit [03b135cebc47: ALSA:
hda - remove dependency on i915 power well for SKL].
However, there are a few exceptional cases where the gfx registers are
accessed from the audio driver: namely the wakeup override bit
toggling at (both system and runtime) resume.  This seems causing a
kernel warning when accessed during the power well down (and likely
resulting in the bogus register accesses).

This patch puts the proper power up / down sequence around the resume
code so that the wakeup bit is fiddled properly while the power is
up.  (The other callback, sync_audio_rate, is used only in the PCM
callback, so it's guaranteed in the power-on.)

Also, by this proper power up/down, the instantaneous flip of wakeup
bit in the resume callback that was introduced by the commit
[033ea349a7cd: ALSA: hda - Fix Skylake codec timeout] becomes
superfluous, as snd_hdac_display_power() already does it.  So we can
clean it up together.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96214
Fixes: 03b135cebc47 ('ALSA: hda - remove dependency on i915 power well for SKL')
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/pci/hda/hda_intel.c | 32 ++++++++++++++++++++------------
 1 file changed, 20 insertions(+), 12 deletions(-)

diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
index 89dacf9b4e6c..160c7f713722 100644
--- a/sound/pci/hda/hda_intel.c
+++ b/sound/pci/hda/hda_intel.c
@@ -906,20 +906,23 @@ static int azx_resume(struct device *dev)
 	struct snd_card *card = dev_get_drvdata(dev);
 	struct azx *chip;
 	struct hda_intel *hda;
+	struct hdac_bus *bus;
 
 	if (!card)
 		return 0;
 
 	chip = card->private_data;
 	hda = container_of(chip, struct hda_intel, chip);
+	bus = azx_bus(chip);
 	if (chip->disabled || hda->init_failed || !chip->running)
 		return 0;
 
-	if (chip->driver_caps & AZX_DCAPS_I915_POWERWELL
-		&& hda->need_i915_power) {
-		snd_hdac_display_power(azx_bus(chip), true);
-		snd_hdac_i915_set_bclk(azx_bus(chip));
+	if (chip->driver_caps & AZX_DCAPS_I915_POWERWELL) {
+		snd_hdac_display_power(bus, true);
+		if (hda->need_i915_power)
+			snd_hdac_i915_set_bclk(bus);
 	}
+
 	if (chip->msi)
 		if (pci_enable_msi(pci) < 0)
 			chip->msi = 0;
@@ -929,6 +932,11 @@ static int azx_resume(struct device *dev)
 
 	hda_intel_init_chip(chip, true);
 
+	/* power down again for link-controlled chips */
+	if ((chip->driver_caps & AZX_DCAPS_I915_POWERWELL) &&
+	    !hda->need_i915_power)
+		snd_hdac_display_power(bus, false);
+
 	snd_power_change_state(card, SNDRV_CTL_POWER_D0);
 
 	trace_azx_resume(chip);
@@ -1008,6 +1016,7 @@ static int azx_runtime_resume(struct device *dev)
 
 	chip = card->private_data;
 	hda = container_of(chip, struct hda_intel, chip);
+	bus = azx_bus(chip);
 	if (chip->disabled || hda->init_failed)
 		return 0;
 
@@ -1015,15 +1024,9 @@ static int azx_runtime_resume(struct device *dev)
 		return 0;
 
 	if (chip->driver_caps & AZX_DCAPS_I915_POWERWELL) {
-		bus = azx_bus(chip);
-		if (hda->need_i915_power) {
-			snd_hdac_display_power(bus, true);
+		snd_hdac_display_power(bus, true);
+		if (hda->need_i915_power)
 			snd_hdac_i915_set_bclk(bus);
-		} else {
-			/* toggle codec wakeup bit for STATESTS read */
-			snd_hdac_set_codec_wakeup(bus, true);
-			snd_hdac_set_codec_wakeup(bus, false);
-		}
 	}
 
 	/* Read STATESTS before controller reset */
@@ -1043,6 +1046,11 @@ static int azx_runtime_resume(struct device *dev)
 	azx_writew(chip, WAKEEN, azx_readw(chip, WAKEEN) &
 			~STATESTS_INT_MASK);
 
+	/* power down again for link-controlled chips */
+	if ((chip->driver_caps & AZX_DCAPS_I915_POWERWELL) &&
+	    !hda->need_i915_power)
+		snd_hdac_display_power(bus, false);
+
 	trace_azx_runtime_resume(chip);
 	return 0;
 }
-- 
2.9.2

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