[alsa-devel] [PATCH v4 08/13] ASoC: Add SoundWire stream programming interface

[Pierre-Louis Bossart]

On 4/24/18 4:06 AM, Vinod Koul wrote:
> On Mon, Apr 23, 2018 at 08:33:08AM -0500, Pierre-Louis Bossart wrote:
>> On 4/21/18 10:58 AM, Vinod Koul wrote:
>>> On Sat, Apr 21, 2018 at 06:59:49AM -0700, Pierre-Louis Bossart wrote:
>>>>
>>>>> +/**
>>>>> + * snd_soc_dai_set_sdw_stream() - Configures a DAI for SDW stream operation
>>>>> + * @dai: DAI
>>>>> + * @stream: STREAM
>>>>> + * @direction: Stream direction(Playback/Capture)
>>>>> + * SoundWire subsystem doesn't have a notion of direction and we reuse
>>>>> + * the ASoC stream direction to configure sink/source ports.
>>>>> + * Playback maps to source on the TX and sink on Rx. Vice-versa for Capture.
>>>>
>>>> this is just confusing...
>>>>
>>>> This should be something like
>>>> "use Playback for source ports and Capture for sink ports".
>>>
>>> Source port on ...? This is also confusing to me!
>>>
>>> For playback there are two ports, one on transmitter aka
>>> TX and one on receiver aka RX. For Tx we use source port, and Rx uses sink
>>> ports. I should probably add port to make people really figure out we are
>>> talking about ports!
>>>
>>> So:
>>>
>>> Playback maps to source port on the TX and sink port on Rx. Vice-versa for Capture.
>>>
>>> Do you agree to above statement?
>>
>> No. Source port and TX are redundant definitions, and your wording isn't
>> clear: is the PLAYBACK/CAPTURE qualifier for the stream or the DAI used by
>> the stream?
> 
> Yes they are redundant, will update. PLAYBACK/CAPTURE qualifier is for stream.

Let me try again.
let's say in point-to-point mode you have dai1 as the source and dai2 as 
the sink.

Which sequence are the higher layers supposed to use:

a.

snd_soc_dai_set_sdw_stream(dai1, stream, PLAYBACK);
snd_soc_dai_set_sdw_stream(dai2, stream, PLAYBACK);

b.

snd_soc_dai_set_sdw_stream(dai1, stream, PLAYBACK);
snd_soc_dai_set_sdw_stream(dai2, stream, CAPTURE);