[alsa-devel] [PATCH v1 3/5] ALSA: hda - Add DP-MST conn list support

[Nikhil Mahale]

On 11/14/19 6:44 PM, Takashi Iwai wrote:
> On Thu, 14 Nov 2019 12:47:36 +0100,
> Nikhil Mahale wrote:
>>
>> On 11/14/19 4:27 PM, Takashi Iwai wrote:
>>> On Thu, 14 Nov 2019 04:37:02 +0100,
>>> Nikhil Mahale wrote:
>>>>
>>>> Document change notification HDA040-A for the Intel High Definition
>>>> Audio 1.0a specification introduces a Device Select verb for Digital
>>>> Display Pin Widgets that are multi-stream capable. This verb selects
>>>> a Device Entry that is used by subsequent Pin Widget verbs,
>>>> including the Get Connection List Entry verb.
>>>>
>>>> This patch queries the current Device Select value, associates it
>>>> with the connection list, and updates the connection list management
>>>> code to consider dev_id along with nid.
>>>
>>> I don't get why this is needed.  This is the list that is added only
>>> from snd_hda_override_conn_list(), and you don't change that call
>>> pattern, so dev_id is always zero.
>>
>> In follow-on patch "ALSA: hda - Add DP-MST support for non-acomp codecs",
>> hdmi_read_pin_conn() calls into snd_hda_set_dev_select() before
>> running into code path -
>>   
>>   snd_hda_get_connections()
>>    |-> snd_hda_get_conn_list()
>>         |-> read_and_add_raw_conns()
>>              |-> snd_hda_override_conn_list()
>>                   |-> add_conn_list()
>>
>> If I understand spec correctly, conn_list need to read/write/track
>> along with device entry set into AC_VERB_SET_DEVICE_SEL verb, right?
> 
> AFAIK, the device connection list itself is same no matter which
> device entry is.  The pin widget may choose the route per device
> entry, but the available routes should be same.

Section 7.3.3.42 of https://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/high-definition-audio-multi-stream.pdf says that 'Get Connection List Entry' control should be per-device!

Thanks,
Nikhil Mahale

> Takashi
> 

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