Re: [PATCH] Genesys Logic UVC microscopes used to work with Linux

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Mon, Jun 07, 2021 at 10:17:35PM +0200, Ricardo Ribalda Delgado wrote:
> Maybe you want to handle this with a quirk? I suspect that some
> devices might work differently with this patches?

Furthermore, for the affected devices, shouldn't the driver cache the
value of the control and apply it only after starting streaming ?
Otherwise a V4L2_S_CTRL() with a new value before streaming will break
the device.

> On Sun, Jun 6, 2021 at 3:36 PM Hans Petter Selasky <hps@selasky.org> wrote:
> >
> > Hi,
> >
> > Some USB video class compliant devices, like Genesys Logic camera chips,
> > used in cheap microscopes, doesn't provide any image if there are UVC
> > SET current value commands for the processing unit, before the camera
> > stream is activated. Fix this by not issuing any UVC SET current value
> > commands, if the value was not changed. This should also work fine with
> > existing UVC compliant webcams and optimized the number of needed
> > processing unit control endpoint requests.
> >
> > Signed-off-by: Hans Petter Selasky <hps@selasky.org>
> >
> > diff --git a/drivers/media/usb/uvc/uvc_ctrl.c
> > b/drivers/media/usb/uvc/uvc_ctrl.c
> > index b3dde98499f4..0d7137eca331 100644
> > --- a/drivers/media/usb/uvc/uvc_ctrl.c
> > +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> > @@ -1697,7 +1697,13 @@ int uvc_ctrl_set(struct uvc_fh *handle,
> >          if (ctrl->info.flags & UVC_CTRL_FLAG_ASYNCHRONOUS)
> >                  ctrl->handle = handle;
> >
> > -       ctrl->dirty = 1;
> > +       /* Avoid setting the current value. */
> > +       if (!ctrl->dirty &&
> > +           memcmp(uvc_ctrl_data(ctrl, UVC_CTRL_DATA_BACKUP),
> > +                  uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT),
> > +                  ctrl->info.size) != 0)
> > +               ctrl->dirty = 1;
> > +
> >          ctrl->modified = 1;
> >          return 0;
> >   }

-- 
Regards,

Laurent Pinchart