Re: [RFC PATCH 2/2] ALSA: hda - HDMI codec driver dynamically attach PCM

[Takashi Iwai <tiwai@suse.de>]

On Fri, 06 Nov 2015 06:33:48 +0100,
Libin Yang wrote:
> 
> Hi Takashi,
> 
> On 11/04/2015 01:38 PM, Libin Yang wrote:
> > On 11/04/2015 12:44 AM, Takashi Iwai wrote:
> >> On Tue, 03 Nov 2015 09:22:53 +0100,
> >> libin.yang@linux.intel.com wrote:
> >>>
> >>> From: Libin Yang <libin.yang@intel.com>
> >>>
> >>> Allocate the PCM based on the number of pin and device entry.
> >>> The number of PCM is pin num plus device entry number per pin.
> >>> For example, on Intel platform, it will be 5 PCMs.
> >>>
> >>> Do not attach the PCM to pin in initialization.
> >>> Dynamically attach PCM to pin when monitor is connected
> >>> in HDMI audio codec driver.
> >>>
> >>> When monitor is disconnected, detach the PCM from the pin.
> >>> And if the audio is playing, stop the playback.
> >>>
> >>> The below is the example of device entry and PCM binding:
> >>> For a monitor is plugged in, we need to dynamically assign
> >>> this monitor to 5 PCM devices (on Intel platform):
> >>> For a monitor at pin nid 0x05, dev index 0, it will prefer PCM 3
> >>> For a monitor at pin nid 0x06, dev index 0, it will prefer PCM 7
> >>> For a monitor at pin nid 0x07, dev index 0, it will prefer PCM 8
> >>> For a monitor at dev index 1 (any pin), it will prefer PCM 9
> >>> For a monitor at dev index 2 (any pin), it will prefer PCM 10
> >>>
> >>> If the preferred PCM is not available, try PCM in this order:
> >>> 9, 10, 3, 7 ,8.
> >>>
> >>> Signed-off-by: Libin Yang <libin.yang@linux.intel.com>
> >>
> >> We should split the changes to a few patches here.  For example,
> >> stopping the stream at discussion is basically an implementation
> >> independent from the MST itself.  IOW, the dynamic attach/detach can
> >> be implemented and tested even without MST support.  Let's code them
> >> at first, then add MST support.
> >
> > This patch actually doesn't depend on MST. I use the dev_num to
> > determine how many PCMs to be created.
> >
> > To Split the patch, how about I create the PCM number based the pin
> > number in the patch?
> >
> >>
> >> Also, it's an open question whether we apply the dynamic attach/detach
> >> to all devices that use the generic hdmi framework.  It means
> >> including AMD and Nvidia.  You hard-coded it to be applied
> >> unconditionally.  Would it break anything potentially...?
> >
> > I have no other verdors platforms to test. But it seems to be OK on
> > other platforms. The impact is, i think, it will stop the stream when
> > monitor is disconnected. Should we apply the code by judging whehter
> > it is Intel platform?
> 
> If you are concerning the impact on other vendors, what about I create 
> a separate mst codec driver? In the driver, I will still use virtual 
> pin, but other vendors platform will not be supported at the moment. 
> Other vendors can add their patches to the new codec driver to support 
> their own mst audio.

No, it's not the option.  Such a behavior change is the big burden to
user-space.  We should provide consistent behavior as much as
possible.


Takashi