[alsa-devel] [PATCH] ALSA: hda - Avoid outputting HDMI audio before prepare() and after close()

[Anssi Hannula]

Some HDMI codecs (at least NVIDIA 0x10de000b:0x10de0101:0x100100) start
transmitting an empty audio stream as soon as PIN_OUT and AC_DIG1_ENABLE
are enabled.

Since commit 6169b673618bf0b2518ce413b54925782a603f06 ("ALSA: hda -
Always turn on pins for HDMI/DP") this happens at first open() time, and
will continue even after close().

Additionally, some codecs (at least Intel PantherPoint HDMI) currently
continue transmitting HDMI audio even after close() in case some actual
audio was output after open() (this happens regardless of PIN_OUT).

Empty HDMI audio transmission when not intended has the effect that a
possible HDMI audio sink/receiver may prefer the empty HDMI audio stream
over an actual audio stream on its S/PDIF inputs.

To avoid the issue before first prepare(), set stream format to 0 on
codec initialization. 0 is not a valid format value for HDMI and will
prevent the audio stream from being output.

Additionally, at close() time, make sure that the stream is cleaned up.
This will ensure that the format is reset to 0 at that time, preventing
audio from being output in that case.

Thanks to OpenELEC developers and users for their help in investigating
this issue on the affected NVIDIA "ION2" hardware, and for the initial
bug report of the issue. Testing of the final version on NVIDIA ION2 was
done by OpenELEC user "MrXIII". Testing on Intel PantherPoint was done
by myself.

Signed-off-by: Anssi Hannula <anssi.hannula at iki.fi>
Cc: stable at vger.kernel.org
---

This also supersedes the patch I attached yesterday as it fixes both
cases.

I guess the alternative to this approach would be to fiddle with
AC_DIG1_ENABLE when preparing and closing the device, but with a quick
look that seemed to be possibly more complex since AC_DIG1_ENABLE is
already meddled with at quite a few places in hda_codec.c.

WDYT, is this OK or should we try a AC_DIG1_ENABLE based approach or
something else?


 sound/pci/hda/patch_hdmi.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/sound/pci/hda/patch_hdmi.c b/sound/pci/hda/patch_hdmi.c
index 807a2aa..bcb83c7 100644
--- a/sound/pci/hda/patch_hdmi.c
+++ b/sound/pci/hda/patch_hdmi.c
@@ -1253,6 +1253,14 @@ static int hdmi_add_cvt(struct hda_codec *codec, hda_nid_t cvt_nid)
 	if (err < 0)
 		return err;
 
+	/*
+	 * Some HDMI codecs (at least NVIDIA 0x10de000b:0x10de0101:0x100100)
+	 * start transmitting an empty audio stream as soon as PIN_OUT and
+	 * AC_DIG1_ENABLE are enabled, which happens at open() time.
+	 * To avoid that, set format to 0, which is not valid for HDMI.
+	 */
+	snd_hda_codec_write(codec, cvt_nid, 0, AC_VERB_SET_STREAM_FORMAT, 0);
+
 	spec->num_cvts++;
 
 	return 0;
@@ -1372,6 +1380,12 @@ static int hdmi_pcm_close(struct hda_pcm_stream *hinfo,
 	struct hdmi_spec_per_pin *per_pin;
 
 	if (hinfo->nid) {
+		/*
+		 * Make sure no empty audio is output after this point by
+		 * setting stream format to 0, which is not valid for HDMI.
+		 */
+		__snd_hda_codec_cleanup_stream(codec, hinfo->nid, 1);
+
 		cvt_idx = cvt_nid_to_cvt_index(spec, hinfo->nid);
 		if (snd_BUG_ON(cvt_idx < 0))
 			return -EINVAL;
-- 
1.7.10