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

[Pierre-Louis Bossart]

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?