[alsa-devel] [RFC PATCH] ASoC: codec: hdac_hdmi: no checking monitor in hw_params

[Yang, Libin]

Hi Pierre,

>-----Original Message-----
>From: Pierre-Louis Bossart [mailto:pierre-louis.bossart at linux.intel.com]
>Sent: Monday, May 6, 2019 11:54 PM
>To: Takashi Iwai <tiwai at suse.de>
>Cc: Yang, Libin <libin.yang at intel.com>; alsa-devel at alsa-project.org;
>broonie at kernel.org; subhransu.s.prusty at intel.com;
>samreen.nilofer at intel.com
>Subject: Re: [alsa-devel] [RFC PATCH] ASoC: codec: hdac_hdmi: no checking
>monitor in hw_params
>
>On 5/6/19 10:50 AM, Takashi Iwai wrote:
>> On Mon, 06 May 2019 17:47:25 +0200,
>> Pierre-Louis Bossart wrote:
>>>
>>> On 5/6/19 10:41 AM, Takashi Iwai wrote:
>>>> On Mon, 06 May 2019 17:37:32 +0200,
>>>> Pierre-Louis Bossart wrote:
>>>>>
>>>>> On 5/6/19 1:59 AM, libin.yang at intel.com wrote:
>>>>>> From: Libin Yang <libin.yang at intel.com>
>>>>>>
>>>>>> This patch move the check of monitor from hw_params to trigger
>callback.
>>>>>>
>>>>>> The original code will check the monitor presence in hw_params. If
>>>>>> the monitor doesn't exist, hw_params will return -ENODEV. Mostly this
>is OK.
>>>>>>
>>>>>> However, pulseaudio will check the pcm devices when kernel is booting
>up.
>>>>>> It will try to open, set hw_params, prepare such pcm devices. We
>>>>>> can't guarantee that the monitor will be connected when kernel is
>booting up.
>>>>>> Especially, hdac_hdmi will export 3 pcms at most. It's hard to say
>>>>>> users will connect 3 monitors to the HDMI/DP ports. This will
>>>>>> cause pulseaudio fail in parsing the pcm devices because the
>>>>>> driver will return -ENODEV in hw_params.
>>>>>>
>>>>>> This patch tries to move the check of monitor presence into
>>>>>> trigger callback. This can "trick" the pulseaudio the pcm is ready.
>>>>>>
>>>>>> This bug is found when we try to enable HDMI detection in
>>>>>> gnome-sound-setting for ASoC hdac_hdmi. After we enable the hdmi
>>>>>> in UCM, pulseaudio will try to parse the hdmi pcm devices. It will
>>>>>> cause failure if there are no monitors connected.
>>>>>
>>>>> Out of curiosity, how is this handled in the legacy driver? I
>>>>> haven't done this for a long time but I remember very clearly being
>>>>> able to play on the HDMI:3,7, etc devices without any monitors
>>>>> connected. You'd get of course no sound but there was no error
>>>>> reported to userspace. The hardware is perfectly capable of pushing
>>>>> samples into the display controller using the HDAudio/iDisp link.
>>>>
>>>> As mentioned in the thread, PA just picks up the stream that is
>>>> connected via a monitor by checking / notified by the corresponding
>>>> Jack control.  On hdac_hdmi driver, the jack control has different
>>>> base name that is irrelevant with the output pins, so PA doesn't
>>>> know how to interpret it, hence it's ignored.
>>>
>>> Yes, but do we have any error checks in the hw_params or trigger
>>> cases with the legacy driver?
>>
>> No, it just continues playing without the actual output.
>
>ok, so could we remove all these error checks then for hdac_hdmi? The
>problem is really the output selection on jack detect/monitor reconfigurations,
>those checks don't add much value, do they?

Yes, I'm planning to remove the checks in hdac_hdmi. Before that, I will 
do some tests on it.

The monitor check in hw_params only impacts on the playback flow.

Regards,
Libin