Re: [PATCH 0/3] UAC2 Gadget: feedback endpoint support

[Glenn Schmottlach <gschmottlach@gmail.com>]

On Thu, Nov 12, 2020 at 6:20 PM Ruslan Bilovol <ruslan.bilovol@gmail.com> wrote:
>
> On Wed, Nov 11, 2020 at 11:30 AM Peter Chen <peter.chen@nxp.com> wrote:
> >
> > On 20-11-08 02:18:28, Ruslan Bilovol wrote:
> > > Current UAC2 gadget implements capture/sync paths
> > > as two USB ISO ASYNC endpoints (IN and OUT).
> > >
> > > This violates USB spec which says that ISO ASYNC OUT endpoint
> > > should have feedback companion endpoint.
> > > See USB2.0 spec  "5.12.4.1 Synchronization Type": asynchronous
> > > sink provides explicit feedback (isochronous pipe).
> > > Interesting that for ISO ASYNC *IN* endpoint respective
> > > feedback isn't required since source provides implicit
> > > feedforward (data stream).
> > >
> > > While it's not an issue if UAC2 Gadget is connected to
> > > Linux host (Linux ignores missing feedback endpoint),
> > > with other hosts like Windows or MacOS the UAC2 Gadget
> > > isn't enumerated due to missing feedback endpoint.
> > >
> > > This patch series adds feedback endpoint support to
> > > UAC2 function, new control to UAC2 mixer which can
> > > be used by userspace tools (like alsaloop from alsa-utils)
> > > for updating feedback frequency reported to the host.
> > > This is useful for usecases when UAC2 Gadget's audio
> > > samples are played to another codec or audio card
> > > with its own internal freerunning clock so host can
> > > be notified that more/less samples are required.
> > >
> > > The alsaloop tool requires some (relatively small)
> > > modifications in order to start support driving
> > > feedback frequency through UAC2 mixer control.
> > > That change will be sent as a separate patch
> > > to ALSA community.
> > >
> > > Also added ability to switch ISO ASYNC OUT endpoint into
> > > adaptive endpoint which doesn't require feedback endpoint
> > > (as per USB spec).
> > >
> > > Ruslan Bilovol (3):
> > >   usb: gadget: f_uac2/u_audio: add feedback endpoint support
> > >   usb: gadget: f_uac2: add adaptive sync support for capture
> > >   usb: gadget: u_audio: add real feedback implementation
> >
> > Hi Ruslan,
> >
> > I applied your patches, but WIN10 still can't recognize it well.
> > The UAC1 is OK for WIN10 with the below same configuration.
> > Any debug information you would like to know to check it?
> >
> >
> > if [ "$FUNC" == "uac2" ]; then
> > mkdir functions/$FUNC".0"
> > echo 2 > functions/$FUNC".0"/p_ssize
> > echo 48000 > functions/$FUNC".0"/p_srate
> > echo 3 > functions/$FUNC".0"/p_chmask
> >
> > echo 2 > functions/$FUNC".0"/c_ssize
> > echo 48000 > functions/$FUNC".0"/c_srate
> > echo 3 > functions/$FUNC".0"/c_chmask
> > #echo 4 > functions/$FUNC".0"/req_number
> > ln -s functions/$FUNC".0" configs/c.1
> > echo high-speed > /sys/kernel/config/usb_gadget/g1/max_speed
> > fi
> >
>
> Hmm... I just tested below config and it works fine with my Win10.
> The only thing I noticed is Windows doesn't enable UAC2 gadget
> by default, but this can be done from Win10 sound settings
>
> --------------------------------->8--------------------------------------
> mkdir cfg
> mount none cfg -t configfs
> mkdir cfg/usb_gadget/g1
> cd cfg/usb_gadget/g1
> mkdir configs/c.1
> mkdir functions/uac2.0
>
> # 44.1 kHz sample rate
> echo 44100 > functions/uac2.0/c_srate
> echo 44100 > functions/uac2.0/p_srate
>
> mkdir strings/0x409
> mkdir configs/c.1/strings/0x409
> echo 0x0101 > idProduct
> echo 0x1d6b > idVendor
> echo my-serial-num > strings/0x409/serialnumber
> echo my-manufacturer > strings/0x409/manufacturer
> echo "Test gadget" > strings/0x409/product
> echo "Conf 1" > configs/c.1/strings/0x409/configuration
> echo 120 > configs/c.1/MaxPower
> ln -s functions/uac2.0 configs/c.1
> echo musb-hdrc.0 > UDC
> --------------------------------->8--------------------------------------
>
> Thanks,
> Ruslan

Hi Ruslan -

With your configuration (above) Win10 was able to recognize and load
the driver. What appears to prevent my configuration from loading is
the fact that I selected 48K as my sample rate and my capture/playback
channel mask includes more than two (2) channels. If I take your
configuration and change the sample rate (c_srate/p_srate) to 48000
Windows will fail to load the driver. Likewise, setting the
c_chmask/p_chmask to 7 (three channels) will also cause the driver to
fail to load.

You mentioned there is an option in Win10 Sound Settings to "enable"
UAC2 by default. I cannot find that option and I wonder if this is
what is preventing me from changing the sample rate or channel mask?
Could Windows be treating my audio gadget as a UAC1 device rather than
a fully multi-channel audio device (even though the usbaudio2.sys
driver is loaded)? Have you tried other configurations to verify your
Win10 box supports more than two channels and a 44.1K sample rate? I
look forward to your feedback and any suggestions you might offer.

Thanks,

Glenn