Re: [PATCH] ALSA: hda/hdmi: Preserve the previous PCM device upon re-enablement

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On Fri, 31 Mar 2023 17:40:46 +0200,
Jaroslav Kysela wrote:
> 
> On 31. 03. 23 17:30, Takashi Iwai wrote:
> 
> > That said, the slot preservation becomes effective only when multiple
> > devices are connected and they are on/off at the same time.  In such a
> > case, the device order may be changed at each screen on/off with the
> > current code, while this patch allows keeping the order.  Maybe I
> > should emphasize about the multiple devices in the patch description.
> 
> I though about possibility to remove a monitor completely. Then you
> can have a gap in the PCM device list.

Do you mean the situation where multiple monitors were connected and
the system is moved afterward to a single monitor environment?  Then
it might be assigned to the second PCM slot, and that's the designed
behavior.  In other cases, as long as only a single monitor is used,
it'll still be assigned to the first PCM slot even with this patch.

> >> The sound server should combine the persistent path only from the ELD
> >> information for the HDMI devices (if present). The problem may be when
> >> multiple similar monitors are connected to the machine. It would be
> >> probably nice to have an unique PCM device name for this usage with
> >> the serial number of the connected monitor (but I don't think it's in
> >> ELD? - it is in the EDID spec thought).
> > 
> > The name string appears actually in the dialog.  But the automatic
> > switch doesn't happen.  So we need some improvement / fix.
> 
> The switch does not happen because PA/PW use the sink/output path
> which use the ALSA PCM device identification. This sink/output path
> also identifies the volume/port preservation. It is not ideal for the
> hotplug audio devices like HDMI, so we should have another way to
> identify those devices. The ALSA's PCM name / subdevice name fields in
> the info structure may be usable for this.

Well, at least, the jack disconnection and re-connection should be
notified in that case, and I thought the switching may happen.
But apparently not.


Takashi



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