[PATCH] uvcvideo: improve error handling in uvc_query_ctrl()

[Hans Verkuil <hverkuil-cisco@xxxxxxxxx>]

- If __uvc_query_ctrl() failed with a non-EPIPE error, then
  report that with dev_err. If an error code is obtained, then
  report that with dev_dbg.

- For error 2 (Wrong state) return -EACCES instead of -EILSEQ.
  EACCES is a much more appropriate error code. EILSEQ will return
  "Invalid or incomplete multibyte or wide character." in strerror(),
  which is a *very* confusing message.

Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
---
Ricardo, this too can be added to the uvc series.
---
 drivers/media/usb/uvc/uvc_video.c | 44 +++++++++++++++++--------------
 1 file changed, 24 insertions(+), 20 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index b63c073ec30e..3f461bb4eeb9 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -68,7 +68,7 @@ int uvc_query_ctrl(struct uvc_device *dev, u8 query, u8 unit,
 			u8 intfnum, u8 cs, void *data, u16 size)
 {
 	int ret;
-	u8 error;
+	u8 error = 0;
 	u8 tmp;

 	ret = __uvc_query_ctrl(dev, query, unit, intfnum, cs, data, size,
@@ -76,35 +76,39 @@ int uvc_query_ctrl(struct uvc_device *dev, u8 query, u8 unit,
 	if (likely(ret == size))
 		return 0;

-	dev_dbg(&dev->udev->dev,
-		"Failed to query (%s) UVC control %u on unit %u: %d (exp. %u).\n",
-		uvc_query_name(query), cs, unit, ret, size);
+	ret = ret < 0 ? ret : -EPIPE;

-	if (ret != -EPIPE)
-		return ret;
-
-	tmp = *(u8 *)data;
+	if (ret == -EPIPE) {
+		tmp = *(u8 *)data;

-	ret = __uvc_query_ctrl(dev, UVC_GET_CUR, 0, intfnum,
-			       UVC_VC_REQUEST_ERROR_CODE_CONTROL, data, 1,
-			       UVC_CTRL_CONTROL_TIMEOUT);
+		ret = __uvc_query_ctrl(dev, UVC_GET_CUR, 0, intfnum,
+				       UVC_VC_REQUEST_ERROR_CODE_CONTROL, data, 1,
+				       UVC_CTRL_CONTROL_TIMEOUT);

-	error = *(u8 *)data;
-	*(u8 *)data = tmp;
+		if (ret == 1)
+			error = *(u8 *)data;
+		*(u8 *)data = tmp;
+		if (ret != 1)
+			ret = ret < 0 ? ret : -EPIPE;
+	}

-	if (ret != 1)
-		return ret < 0 ? ret : -EPIPE;
+	if (error)
+		dev_dbg(&dev->udev->dev,
+			"Failed to query (%s) UVC control %u on unit %u: got error %u.\n",
+			uvc_query_name(query), cs, unit, error);
+	else
+		dev_err(&dev->udev->dev,
+			"Failed to query (%s) UVC control %u on unit %u: %d (exp. %u).\n",
+			uvc_query_name(query), cs, unit, ret, size);

-	uvc_dbg(dev, CONTROL, "Control error %u\n", error);
+	if (!error)
+		return ret;

 	switch (error) {
-	case 0:
-		/* Cannot happen - we received a STALL */
-		return -EPIPE;
 	case 1: /* Not ready */
 		return -EBUSY;
 	case 2: /* Wrong state */
-		return -EILSEQ;
+		return -EACCES;
 	case 3: /* Power */
 		return -EREMOTE;
 	case 4: /* Out of range */
-- 
2.30.0