[media] uvcvideo: Ignore GET_RES error for XU controls

GET_RES request support is mandatory for extension units, but some
cameras still choke on it (one example is the Logitech QuickCam PTZ that
returns a single byte for the PTZ relative control instead of four).

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

2 files changed, 16 insertions, 2 deletions

diff --git a/drivers/media/video/uvc/uvc_ctrl.c b/drivers/media/video/uvc/uvc_ctrl.c
index 254d32688843..3e849d977bd4 100644
--- a/drivers/media/video/uvc/uvc_ctrl.c
+++ b/drivers/media/video/uvc/uvc_ctrl.c
@@ -878,8 +878,21 @@ static int uvc_ctrl_populate_cache(struct uvc_video_chain *chain,
                                      chain->dev->intfnum, ctrl->info.selector,
                                      uvc_ctrl_data(ctrl, UVC_CTRL_DATA_RES),
                                      ctrl->info.size);
-                if (ret < 0)
-                        return ret;
+                if (ret < 0) {
+                        if (UVC_ENTITY_TYPE(ctrl->entity) !=
+                            UVC_VC_EXTENSION_UNIT)
+                                return ret;
+
+                        /* GET_RES is mandatory for XU controls, but some
+                         * cameras still choke on it. Ignore errors and set the
+                         * resolution value to zero.
+                         */
+                        uvc_warn_once(chain->dev, UVC_WARN_XU_GET_RES,
+                                      "UVC non compliance - GET_RES failed on "
+                                      "an XU control. Enabling workaround.\n");
+                        memset(uvc_ctrl_data(ctrl, UVC_CTRL_DATA_RES), 0,
+                               ctrl->info.size);
+                }
         }
 
         ctrl->cached = 1;
diff --git a/drivers/media/video/uvc/uvcvideo.h b/drivers/media/video/uvc/uvcvideo.h
index 882159aab610..2b84cbb49665 100644
--- a/drivers/media/video/uvc/uvcvideo.h
+++ b/drivers/media/video/uvc/uvcvideo.h
@@ -477,6 +477,7 @@ struct uvc_driver {
 
 #define UVC_WARN_MINMAX         0
 #define UVC_WARN_PROBE_DEF      1
+#define UVC_WARN_XU_GET_RES     2
 
 extern unsigned int uvc_clock_param;
 extern unsigned int uvc_no_drop_param;