Re: [RFC PATCH v2 09/22] ASoC: qcom: qdsp6: Introduce USB AFE port to q6dsp

[Wesley Cheng]

Hi Pierre,

On 1/26/2023 7:38 AM, Pierre-Louis Bossart wrote:
> On 1/25/23 21:14, Wesley Cheng wrote:
> > The QC ADSP is able to support USB playback endpoints, so that the main
> > application processor can be placed into lower CPU power modes.  This adds
> > the required AFE port configurations and port start command to start an
> > audio session.
> >
> > Specifically, the QC ADSP can support all potential endpoints that are
> > exposed by the audio data interface.  This includes, feedback endpoints
> > (both implicit and explicit) as well as the isochronous (data) endpoints.
> > The size of audio samples sent per USB frame (microframe) will be adjusted
> > based on information received on the feedback endpoint.
>
> I think you meant "support all potential endpoint types"
>
> It's likely that some USB devices have more endpoints than what the DSP
> can handle, no?

True, as we discussed before, we only handle the endpoints for the audio 
interface.  Other endpoints, such as HID, or control is still handled by 
the main processor.

> And that brings me back to the question: what is a port and the
> relationship between port/backend/endpoints?
>
> Sorry for being picky on terminology, but if I learned something in days
> in standardization it's that there shouldn't be any ambiguity on
> concepts, otherwise everyone is lost at some point.

No worries, I can understand where you're coming from :).  After 
re-reading some of the notations used, I can see where people may be 
confused.

> >   static struct afe_port_map port_maps[AFE_PORT_MAX] = {
> > +	[USB_RX] = { AFE_PORT_ID_USB_RX, USB_RX, 1, 1},
> >   	[HDMI_RX] = { AFE_PORT_ID_MULTICHAN_HDMI_RX, HDMI_RX, 1, 1},
> >   	[SLIMBUS_0_RX] = { AFE_PORT_ID_SLIMBUS_MULTI_CHAN_0_RX,
> >   				SLIMBUS_0_RX, 1, 1},
>
> And if I look here a port seems to be a very specific AFE concept
> related to interface type? Do we even need to refer to a port in the USB
> parts?

Well, this is a design specific to how the Q6 AFE is implemented.  There 
is a concept for an AFE port to be opened.  However, as mentioned 
earlier, the "port" term used in soc-usb should be more for how many USB 
devices can be supported.

If there was a case the audio DSP would support more than one USB 
device, I believe another AFE port would need to be added.

Thanks
Wesley Cheng