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

[Hans Petter Selasky <hps@xxxxxxxxxxx>]

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@xxxxxxxxxxx>

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;
 }