Hi Pierre,
On 1/30/2023 3:59 PM, Pierre-Louis Bossart wrote:
On 1/30/23 16:54, Wesley Cheng wrote:
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.
The number of isoc/audio endpoints can be larger than 1 per direction,
it's not uncommon for a USB device to have multiple connectors on the
front side for instruments, mics, monitor speakers, you name it. Just
google 'motu' or 'rme usb' and you'll see examples of USB devices that
are very different from plain vanilla headsets.
Thanks for the reference.
I tried to do some research on the RME USB audio devices, and they
mentioned that they do have a "class compliant mode," which is for
compatibility w/ Linux hosts. I didn't see a vendor specific USB SND
driver matching the USB VID/PID either, so I am assuming that it uses
the USB SND driver as is.(and that Linux doesn't currently support their
vendor specific mode) In that case, the device should conform to the
UAC2.0 spec (same statement seen on UAC3.0), which states in Section
4.9.1 Standard AS Interface Descriptor Table 4-26:
"4 bNumEndpoints 1 Number Number of endpoints used by this
interface (excluding endpoint 0). Must be
either 0 (no data endpoint), 1 (data
endpoint) or 2 (data and explicit feedback
endpoint)."
So each audio streaming interface should only have 1 data and
potentially 1 feedback. However, this device does expose a large number
of channels (I saw up to 18 channels), which the USB backend won't be
able to support. I still need to check how ASoC behaves if I pass in a
profile that the backend can't support.
Maybe in the non-class compliant/vendor based class driver, they have
the support for multiple EPs per data interface? I don't have one of
these devices on hand, so I can't confirm that.
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.
would the suggested infrastructure work though, even if the DSP could
deal with multiple endpoints on different devices ? You have static
mutexes and ops, can that scale to more than one USB device?
The mutex is only for registering the card, and ensuring atomic access
to the list. I don't see how that would block support for having
multiple devices being registered to soc-usb. ops are stored per
backend device.
Greg did want me to re-look at the soc-usb device management, so I will
have to rework some of these things. It would be nice to see if we can
get it to work like how the headphone jack works, ie interaction between
soc-jack and core/jack.c.
Thanks
Wesley Cheng
