Ignored USB-audio implicit feedback in kernel 5.8rc3

[Takashi Iwai]

On Tue, 07 Jul 2020 12:03:25 +0200,
Pavel Hofman wrote:
> 
> Hi Takashi,
> 
> Dne 07. 07. 20 v 11:40 Takashi Iwai napsal(a):
> > On Fri, 03 Jul 2020 12:17:14 +0200,
> > Pavel Hofman wrote:
> >>
> >>
> >> Dne 02. 07. 20 v 13:28 Pavel Hofman napsal(a):
> >>>
> >>>
> >>> Please is the requirement that EP OUT + EP IN implicit feedback data
> >>> must be in the same interface really necessary? If such a requirement
> >>> was dropped, IMO many devices could be removed from the existing
> >>> set_sync_ep_implicit_fb_quirk and many devices would work out of the
> >>> box,
> >>
> >> I am still thinking about the single-interface requirement. If both
> >> endpoints were to be part of a single interface, could they use
> >> different altsettings for different sample lengths for capture and
> >> playback? E.g. to save USB bandwidth when the capture is used only for
> >> implicit feedback - capturing at 16bits, playback at 32bits.
> >>
> >> In the quirked XMOS devices the common clock for both directions is
> >> defined by the clock feature, the altsettings for each direction (in
> >> separate interfaces) are used for setting sample length.
> >
> > Could you check for-linus branch of my sound git tree?
> > Just to be sure whether you're hitting the issue that has been already
> > addressed.
> >
> 
> I developed the RTX6001 patch on 5.8-rc3 kernel, and commits since
> that tag in
> https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/log/?h=for-linus
> do not seem to address the issue.
> 
> I think the generic code searching for the implicit-feedback endpoint
> works only on the current interface (alts)
> https://github.com/tiwai/sound/blob/master/sound/usb/pcm.c#L491
> 
> I do not know if searching for IN endpoints with the same number and
> USB_ENDPOINT_USAGE_IMPLICIT_FB mask in other interfaces is
> correct. But it seems to me it would yield correct results for a
> number of existing quirks in set_sync_ep_implicit_fb_quirk (typically
> those setting ep=0x81).

Yeah I found your patch later.  Now it's in for-linus branch, too.


Takashi