Support for NUX MG-300 USB interface

[Mike Oliphant]

Unfortunately, the "uac_clock_selector_set_val()" call does not seem to
change anything.

>From doing some more testing, I think that the references to clock id "40"
are ok - it has "40" stored in fmt->clock, but when it uses it,
"__uac_clock_find_source()" gets called and it resolved to the actual clock
source - "41".

Not sure about the "No valid sample rate available for 1:1, assuming a
firmware bug" error, but I suspect it is spurious.
"check_valid_altsetting_v2v3()" is failing for some reason, but it is
ignoring the error.

Playback is completely silent, but the system seems to think it is working.
No apparent errors, and a play operation seems to take the correct amount
of time. Just no audio.

Maybe it is a mixer issue? mixer.c is putting out "RANGE setting not yet
supported" errors on startup.

Here is a sample of dmesg output for a playback session:

[ 4748.260975] usb 1-1.3: Open EP 0x1, iface=1:1, idx=0
[ 4748.260983] usb 1-1.3:   channels=2, rate=48000, format=S32_LE,
period_bytes=48000, periods=4, implicit_fb=0
[ 4748.260988] usb 1-1.3: Open EP 0x81, iface=1:1, idx=1
[ 4748.260992] usb 1-1.3:   channels=2, rate=48000, format=S32_LE,
period_bytes=48000, periods=4, implicit_fb=0
[ 4748.260996] usb 1-1.3: Setting usb interface 1:0 for EP 0x1
[ 4748.261320] usb 1-1.3: 1:1 Set sample rate 48000, clock 40
[ 4748.261873] usb 1-1.3: Setting params for data EP 0x1, pipe 0x9d00
[ 4748.261890] usb 1-1.3: Set up 12 URBS, ret=0
[ 4748.261897] usb 1-1.3: Setting usb interface 1:1 for EP 0x1
[ 4748.262097] usb 1-1.3: Setting params for sync EP 0x81, pipe 0x9d80
[ 4748.262105] usb 1-1.3: Set up 4 URBS, ret=0
[ 4748.262147] usb 1-1.3: Starting data EP 0x1 (running 0)
[ 4748.262180] usb 1-1.3: 12 URBs submitted for EP 0x1
[ 4748.262183] usb 1-1.3: Starting sync EP 0x81 (running 0)
[ 4748.262193] usb 1-1.3: 4 URBs submitted for EP 0x81
[ 4748.262311] usb 1-1.3: 1:1 Start Playback PCM
[ 4762.887812] usb 1-1.3: Stopping sync EP 0x81 (running 1)
[ 4762.887836] usb 1-1.3: Stopping data EP 0x1 (running 1)
[ 4762.887849] usb 1-1.3: 1:1 Stop Playback PCM
[ 4762.902542] usb 1-1.3: Closing EP 0x1 (count 1)
[ 4762.902549] usb 1-1.3: Setting usb interface 1:0 for EP 0x1
[ 4762.902915] usb 1-1.3: EP 0x1 closed
[ 4762.902928] usb 1-1.3: Closing EP 0x81 (count 1)
[ 4762.902935] usb 1-1.3: Setting usb interface 1:0 for EP 0x81
[ 4762.903179] usb 1-1.3: EP 0x81 closed

On Mon, Jan 18, 2021 at 1:59 PM Takashi Iwai <tiwai at suse.de> wrote:

> On Mon, 18 Jan 2021 22:15:26 +0100,
> Mike Oliphant wrote:
> >
> > Progress - thanks for the patch!
> >
> > That got rid of the clock errors, and the the device now reports a 48000
> > sample rate, which is correct.
> >
> > Unfortunately, it still isn't working properly. Playback doesn't seem to
> work
> > at all. Capture kind of works - it does record, but the audio is
> extremely
> > noisy.
> >
> > Here is the current dmesg output when the device is connected.
> >
> > Notable is the error "No valid sample rate available for 1:1, assuming a
> > firmware bug".
> >
> > Also notable is "1:1 Set sample rate 48000, clock 40" - where "40" is
> the id
> > of the clock selector - "41" is the id of the actual clock source. So
> maybe
> > something is still getting wired up wrong?
>
> OK, how about the one below instead?
>
>
> Takashi
>
> --- a/sound/usb/clock.c
> +++ b/sound/usb/clock.c
> @@ -298,6 +298,12 @@ static int __uac_clock_find_source(struct
> snd_usb_audio *chip,
>         if (selector) {
>                 int ret, i, cur;
>
> +               if (selector->bNrInPins == 1) {
> +                       uac_clock_selector_set_val(chip,
> selector->bClockID, 1);
> +                       ret = 1;
> +                       goto find_source;
> +               }
> +
>                 /* the entity ID we are looking for is a selector.
>                  * find out what it currently selects */
>                 ret = uac_clock_selector_get_val(chip, selector->bClockID);
> @@ -314,6 +320,7 @@ static int __uac_clock_find_source(struct
> snd_usb_audio *chip,
>                         return -EINVAL;
>                 }
>
> +       find_source:
>                 cur = ret;
>                 ret = __uac_clock_find_source(chip, fmt,
>                                               selector->baCSourceID[ret -
> 1],
>