Implicit feedback on BOSS GT-1, the saga continues...

[Mike Oliphant]

Hi Lucas,

Your observation that the Roland D-05 still needs the capture feedback made
me try some more testing, and I think the GT-1 actually is the same.

I use my device with jackd running for both capture/playback at the same
time. This works for me without capture feedback enabled. But, it turns out
that just doing an "arecord" without playback fails. Enabling the capture
feedback makes capture also work without playback (and everything else
still works perfectly).

Given this, I agree that it seems likely that most, if not all, of these
Roland devices work the same way. It would be great to get more devices
tested, though.

As to an actual patch, I think it is probably best left to Takashi to
decide if he is comfortable with making a change to
snd_usb_endpoint_start() in endpoint.c, and if so, how he wants to make it
conditional for devices - whether an ID check in endpoint.c, or a flag on
feedback setup, or some other way.

Mike

On Thu, Apr 8, 2021 at 9:55 PM Lucas <jaffa225man at gmail.com> wrote:

> Geraldo, you've made testing kernel patches for me quite easy, so thanks
> to you!  And I'm happy to report that your patch, which I manually applied
> because I forgot to remove the "if (false)" change, is working perfectly!
> I am now able to use the, minimally mentioned, Takashi UA-101 MIDI patch
> with the UA-101 set to USB 1.1 mode, on the same kernel that has perfectly
> clean Boutique D-05 playback.  The Takashi UA-101 patch is here:
> https://bugzilla.kernel.org/show_bug.cgi?id=212477, just in case there's
> curiosity.  :)
>
> It seems to me, that since the UA-101 in (USB 1.1 mode) isn't compatible
> with the "if (false)" endpoint.c method, it would have to be matched for
> exclusion, assuming we would ever be able to more simply match with
> Roland's/BOSS' Vendor ID of 0x0582.  I still think that would be the
> ultimate patch because, as far as I'm aware, all new Roland/BOSS devices
> use minimally-differing forms of this implicit feedback quirk.
>
> Thanks. again, for everything Mike, Geraldo, & Takashi!
>
>   Lucas
>