The uvc_set_ctrl() calls don't write to the hardware. A failure at that
point thus leaves the device in a clean state, with no control modified.
Set the error_idx field to the count value to reflect that, as per the
V4L2 specification.

TRY_EXT_CTRLS is unchanged and the error_idx field must always be set to
the failed control index in that case.

Signed-off-by: Laurent Pinchart <laurent.pinch...@ideasonboard.com>
Acked-by: Hans Verkuil <hans.verk...@cisco.com>
---
 drivers/media/usb/uvc/uvc_v4l2.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
index 5eb8989..68d59b5 100644
--- a/drivers/media/usb/uvc/uvc_v4l2.c
+++ b/drivers/media/usb/uvc/uvc_v4l2.c
@@ -685,7 +685,8 @@ static long uvc_v4l2_do_ioctl(struct file *file, unsigned 
int cmd, void *arg)
                        ret = uvc_ctrl_set(chain, ctrl);
                        if (ret < 0) {
                                uvc_ctrl_rollback(handle);
-                               ctrls->error_idx = i;
+                               ctrls->error_idx = cmd == VIDIOC_S_EXT_CTRLS
+                                                ? ctrls->count : i;
                                return ret;
                        }
                }
-- 
1.7.8.6

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