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

Anssi Hannula anssi.hannula at iki.fi
Sun Feb 17 18:57:57 CET 2013

On Sunday, February 17, 2013, Takashi Iwai <tiwai at suse.de> wrote:
> At Sun, 17 Feb 2013 14:23:21 +0200,
> Anssi Hannula wrote:
>> 17.02.2013 10:24, Takashi Iwai kirjoitti:
>> > At Sat, 16 Feb 2013 22:59:40 +0200,
>> > Anssi Hannula wrote:
>> >>
>> >> 16.02.2013 18:40, Anssi Hannula kirjoitti:
>> >>> Some HDMI codecs (at least NVIDIA 0x10de000b:0x10de0101:0x100100)
>> >>> transmitting an empty audio stream as soon as PIN_OUT and
>> >>> are enabled.
>> >>>
>> >>> Since commit 6169b673618bf0b2518ce413b54925782a603f06 ("ALSA: hda -
>> >>> Always turn on pins for HDMI/DP") this happens at first open() time,
>> >>> will continue even after close().
>> >>>
>> >>> Additionally, some codecs (at least Intel PantherPoint HDMI)
>> >>> continue transmitting HDMI audio even after close() in case some
>> >>> 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
>> >>> 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
>> >>> This will ensure that the format is reset to 0 at that time,
>> >>> audio from being output in that case.
>> >>>
>> >>> Thanks to OpenELEC developers and users for their help in
>> >>> this issue on the affected NVIDIA "ION2" hardware, and for the
>> >>> bug report of the issue. Testing of the final version on NVIDIA ION2
>> >>> done by OpenELEC user "MrXIII". Testing on Intel PantherPoint was
>> >>> 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
>> >>> 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.
>> >>
>> >> Hmm... actually, that would not be so much more complex, just making
>> >> sure AC_DIG1_ENABLE is off in hdmi_add_cvt() (by e.g. zeroing
>> >> AC_VERB_SET_DIGI_CONVERT_1) and making snd_hda_spdif_ctls_unassign()
>> >> call "set_spdif_ctls(codec, spdif->nid, 0, -1);".
>> >>
>> >> However, it would still mean that just a simple snd_pcm_open() could
>> >> cause an empty stream to be output (if format is valid), since iec958
>> >> controls are assigned at open() time, and iec958 mute controls
>> >> AC_DIG1_ENABLE. Or we could add additional code in hda_codec.c to
>> >> prevent AC_DIG1_ENABLE being set if prepare() has not been called.
>> >
>> > Is the problem fixed if you set codec->no_sticky_stream = 1?
>> The issue on NVIDIA reported by users, no, that flag is not used in a
>> simple open()+close() path.
> It is.  The flag is used in hda_codec.c.  It's a flag for setting
> FORMAT stuff, not the SPDIF status.

The only use I see there is in __snd_hda_codec_cleanup_stream(), but AFAICS
that is not called by open/close callbacks of hdmi, since the stream is
only allocated in prepare(). Am I missing something?

>> My issue on Intel, yes.
>> > Actually, the current behavior is intentional.  There have been bug
>> > reports that just reopening a device causes the receiver not reacting
>> > immediately.  In the worst case, it takes a few seconds to sync. So we
>> > introduced a mechanism to keep the PCM stream assignment.
>> Hmm.. If the intention is to keep a silent stream playing even after
>> device has been closed, why was PIN_OUT disabled on close until "ALSA:
>> hda - Always turn on pins for HDMI/DP" in December?
> The intention isn't to keep the stream playing, but it keeps the
> STREAM tag.  It's just a weird hardware implementation that it keeps
> playing.  And, the feature was implemented far before the new dynamic
> SPDIF status control assignment and the dynamic pin down.  So, it got
> broken by that stuff sometime ago.

Ah, so you mean something different with „lost sync„, I used that
interchangeably with „hdmi stream stopped„.  Can you explain the
difference, to get us on the same page? :)

I was able to see only two states on the receiver. Either the HDMI icon is
on (and any simultaneously active s/pdif is ignored by default unless
otherwise configured), or it is off (after which starting the playback
again takes approx. 0.8sec). But is there a more subtle 3rd state? (Or
maybe the behavior depends on the receiver, and my receiver handles more
situations like the stream is active).

>> Anyway, I can understand the desire to keep an empty stream running
>> after device has been closed. However, IMO a simple
>> snd_pcm_open+snd_pcm_close triggering a start of empty stream (as on the
>> affected NVIDIA hw) seems wrong, since this can happen without actual
>> audio being output by application device probing (e.g. pulseaudio) and
>> the HDMI audio supersedes actual audio, as reported by several users
>> (during beta/rc testing of OpenELEC - it is also not very obvious what
>> is causing the sudden brokenness of audio, it took quite a bit of
>> debugging before we found out the cause).
> Again, the intention isn't about keep stream sending.  It was a
> workaround to avoid the unnecessary out-of-sync situation at each open
> or prepare.  Otherwise you'll get a few seconds silence at each
> stream.

OK, I thought not sending stream and out-of-sync are the same thing.

>> Also, as noted, this "current behavior" doesn't actually work on the
>> affected NVIDIA 0b hardware (nor it does on my non-affected NVIDIA 0b
>> hardware); when the actual audio stream stops, sync is lost regardless
>> of the kept stream assignment.
> Yes, this got broken by the update sometime ago, unfortunately.
> And, remember that user may still use OSS emulation -- in that case,
> there are frequent open/close sequences.  So, keeping sync after close
> makes sense for such.
> In other words, there is no black/white solution for this problem.
> It must be somehow configurable for each use case.
>> > If your problem is solved by clearing codec->no_stick_stream, we may
>> > provide an additional mixer control to turn it on/off, for example,
>> > because we can't blindly disable/enable it globally if user's receiver
>> > has a problem with the stream sync.
>> I think we definitely should make "no empty hdmi stream after close or
>> before first open" an option at least.
>> However, while writing this I made some tests on my hw with NVIDIA 15
>> codec, and it seems to have a fourth different set of behavior related
>> to this.
>> So we now have at least (unless I made a mistake at some point, which is
>> not too unlikely considering the amount of variables here... I can
>> retest stuff if needed):
>> NVIDIA 0b non-"ION2" (rev 0x100100) hardware:
>> - HDMI output becomes active when the real audio stream starts
>>   (plus non-tested other conditions, at least AC_DIG1_ENABLE)
>> - HDMI output stops after the real audio stream stops
>> - on cold start: format is valid, AC_DIG1_ENABLE is off
>> => currently HDMI becomes active when actual audio is output, and
>>    is stopped when audio stops (e.g. even when pausing playback without
>>    closing)
>> NVIDIA 0b "ION2" (rev 0x100200) hardware:
>> - HDMI output becomes active when PIN_OUT + AC_DIG1_ENABLE + valid
>>   stream format
>> - HDMI output stops after the real audio stream stops
>>   (it would follow that flipping AC_DIG1_ENABLE off and on again
>>    would start HDMI output again - however, not tested)
>> - on cold start: format is valid, AC_DIG1_ENABLE is off
>> => currently HDMI becomes active immediately at open(), and is stopped
>>    when actual audio stream stops. However, in case of open()+close(),
>>    the actual audio stream never starts and therefore never stops,
>>    leaving the HDMI audio active with empty stream
>> NVIDIA 15 hardware:
>> - HDMI output becomes active when PIN_OUT + AC_DIG1_ENABLE
>>   (no valid stream format needed)
>> - HDMI output stops after the above conditions stop
>> - on cold start: format is valid, AC_DIG1_ENABLE is off
>> => currently HDMI becomes active immediately at open(),
>>    and is never stopped unless it is muted during playback
>>    (and my earlier patch would not actually change that)
>> Intel PantherPoint HDMI hardware:
>> - HDMI output becomes active when AC_DIG1_ENABLE + valid stream format
>>   (regardless of PIN_OUT)
>> - HDMI output stops after the above conditions stop (or, in a strange
>>   just-trying-to-confuse-me way, when stopping a 32kHz stream for some
>>   reason)
>> - on cold start: format is invalid, AC_DIG1_ENABLE is on
>> => currently HDMI becomes active when the stream format is set for
>>    the first time, i.e. something is played back. It is never stopped
>>    unless it is muted during playback.
>> Note that e.g. pulseaudio opens+closes devices immediately, so on NVIDIA
>> 0b "ION2" and NVIDIA 15 cases HDMI output becomes active immediately.
>> Also note that muting the IEC958 control won't stop the HDMI output
>> unless/until the device is actually opened, since the IEC958 ctl is
>> nowadays only assigned to the device when opened.
>> Now, whatever is the behavior that we want, according the above clearly
>> there is space for improvement in any case.
>> For example, when exactly do we want the HDMI port to become active,
>> preferably?
>> - immediately, always on initialization
>> - on first open()
>> - on first prepare()
>> And when to stop?
>> - never
>> - on close()
>> - after timeout after close()
> We just need to try.  I guess the setting at open() is the cleanest
> way of implementation.  The delayed cleanup sounds interesting, and if
> it can be implemented without too many mess, this looks like the best
> option for stopping.
>> As per the above test data most hardware can be made to follow any of
>> the behaviors (except that NVIDIA 0b non-ION2 cannot seemingly support
>> keeping empty HDMI stream open at all, at least per current tests), but
>> the current behavior is rather mixed.
>> As you probably have gathered, I'd support HDMI port to become active at
>> prepare() (after all we don't have the stream parameters yet at open
>> time or earlier), and to become inactive at close(). I guess I can
>> settle for an option, though, if you insist :)
>> (There is also the power saving stuff to be considered, but I'm ignoring
>> that simply because I have no information about the effects there...)
> It shouldn't influence so much on the power.  The empty audio stream
> has nothing to do with the sound driver side.  The sound component can
> be even completely powered off during the empty audio stream is
> embedded into HDMI/DP frame.
> thanks,
> Takashi

Anssi Hannula

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