Re: [RFC PATCH] ASoC: codec: hdac_hdmi: no checking monitor in hw_params

[Takashi Iwai <tiwai@suse.de>]

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@intel.com wrote:
> >>> From: Libin Yang <libin.yang@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.


Takashi