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

[Nikhil Mahale]

Thanks,
Nikhil Mahale

On 11/15/19 4:00 PM, Takashi Iwai wrote:
> On Fri, 15 Nov 2019 10:52:30 +0100,
> Nikhil Mahale wrote:
>>
>> 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!
> 
> Hrm, right.  It's a bit concern that this may lead to the unlimited
> number of data, though.
> 
> Since the necessity is only for HDMI codec, if that's the only place
> we need the connection list, the call there can be replaced with
> snd_hda_get_raw_connections() so that the result won't be cached in
> HD-audio core side.
Ok, I am addressing this in 3rd version of patch set.

Thanks,
Nikhil Mahale

> Takashi
> 

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