Re: [RFC PATCH v2 11/22] ASoC: qcom: Add USB backend ASoC driver for Q6

[Pierre-Louis Bossart]

>>> +static struct snd_soc_dai_driver q6usb_be_dais[] = {
>>> +    {
>>> +        .playback = {
>>> +            .stream_name = "USB BE RX",
>>> +            .rates = SNDRV_PCM_RATE_8000 | SNDRV_PCM_RATE_11025 |
>>> +                SNDRV_PCM_RATE_16000 | SNDRV_PCM_RATE_22050 |
>>> +                SNDRV_PCM_RATE_32000 | SNDRV_PCM_RATE_44100 |
>>> +                SNDRV_PCM_RATE_48000 | SNDRV_PCM_RATE_96000 |
>>> +                SNDRV_PCM_RATE_192000,
>>> +            .formats = SNDRV_PCM_FMTBIT_S16_LE |
>>> SNDRV_PCM_FMTBIT_S16_BE |
>>> +                SNDRV_PCM_FMTBIT_U16_LE | SNDRV_PCM_FMTBIT_U16_BE |
>>> +                SNDRV_PCM_FMTBIT_S24_LE | SNDRV_PCM_FMTBIT_S24_BE |
>>> +                SNDRV_PCM_FMTBIT_U24_LE | SNDRV_PCM_FMTBIT_U24_BE,
>>> +            .channels_min = 1,
>>> +            .channels_max = 2,
>>> +            .rate_max =     192000,
>>> +            .rate_min =    8000,
>>> +        },
>>> +        .id = USB_RX,
>>> +        .name = "USB_RX_BE",
>>> +        .ops = &q6usb_ops,
>>> +    },
>>> +};
>>
>> ... here I see a single DAI, so presumably ONE endpoint can be supported?
>>
> 
> One USB audio device can be supported.
> one AFE port = one USB audio device
> 
>> I didn't see in the rest of the code how a card with multiple endpoint
>> would be rejected, nor how the capabilities are checked?
>>
> 
> Need to take a look at this query a bit more.  Let me try to pass in a
> format that can't be supported by the audio DSP, and see if the formats
> specified in this structure will not allow userspace to start the session.
> 
> When you say a "card with multiple endpoints" are you referring to a USB
> device that exposes multiple data (ISOC let's say) eps for its data
> interface?  I haven't run into a device like that.

A headset will typically only have two isoc endpoints for playback and
capture respectively, but while that's a very large market USB audio is
far from restricted to this configuration. It's not uncommon for the pro
or prosumer market to see devices with multiple input/output
capabilities and run-time mixing on the host.