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

[Libin Yang <libin.yang@linux.intel.com>]

Hi Takashi,

On 11/06/2015 05:12 PM, Takashi Iwai wrote:
> 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.

OK, I see. What do you think if I judge the platform before using DP 
MST mode?

Best Regards,
Libin

>
>
> Takashi
>