[PATCH] uvcvideo: extend UVC_QUIRK_FIX_BANDWIDTH to MJPEG streams

[Pavel Rojtberg]

From: Pavel Rojtberg <rojtb...@gmail.com>

attaching two Logitech C615 webcams currently results in
    VIDIOC_STREAMON: No space left on device
as the required bandwidth is not estimated correctly by the device.
In fact it always requests 3060 bytes - no matter the format or resolution.

setting UVC_QUIRK_FIX_BANDWIDTH does not help either as it is only implemented
for uncompressed streams.

This patch extends UVC_QUIRK_FIX_BANDWIDTH to MJPEG streams by making a
(conservative) assumption of 4bpp for MJPEG streams.
As the actual compression ration is often closer to 1bpp this can be overridden
 via the new mjpeg_bpp parameter.

Based on:
https://www.mail-archive.com/linux-uvc-devel@lists.berlios.de/msg05724.html
---
 drivers/media/usb/uvc/uvc_driver.c | 14 +++++++++++++-
 drivers/media/usb/uvc/uvc_video.c  |  3 ++-
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_driver.c 
b/drivers/media/usb/uvc/uvc_driver.c
index 70842c5..f7b759e 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -37,6 +37,7 @@ unsigned int uvc_no_drop_param;
 static unsigned int uvc_quirks_param = -1;
 unsigned int uvc_trace_param;
 unsigned int uvc_timeout_param = UVC_CTRL_STREAMING_TIMEOUT;
+static unsigned int uvc_mjpeg_bpp_param;
 
 /* ------------------------------------------------------------------------
  * Video formats
@@ -463,7 +464,16 @@ static int uvc_parse_format(struct uvc_device *dev,
                strlcpy(format->name, "MJPEG", sizeof format->name);
                format->fcc = V4L2_PIX_FMT_MJPEG;
                format->flags = UVC_FMT_FLAG_COMPRESSED;
-               format->bpp = 0;
+               if ((uvc_mjpeg_bpp_param >= 1) && (uvc_mjpeg_bpp_param <= 16)) {
+                       format->bpp = uvc_mjpeg_bpp_param;
+               } else {
+                       /* conservative estimate. Actual values are around 1bpp.
+                        * see e.g.
+                        * 
https://developers.google.com/speed/webp/docs/webp_study
+                        */
+                       format->bpp = 4;
+               }
+
                ftype = UVC_VS_FRAME_MJPEG;
                break;
 
@@ -2274,6 +2284,8 @@ module_param_named(trace, uvc_trace_param, uint, 
S_IRUGO|S_IWUSR);
 MODULE_PARM_DESC(trace, "Trace level bitmask");
 module_param_named(timeout, uvc_timeout_param, uint, S_IRUGO|S_IWUSR);
 MODULE_PARM_DESC(timeout, "Streaming control requests timeout");
+module_param_named(mjpeg_bpp, uvc_mjpeg_bpp_param, uint, S_IRUGO|S_IWUSR);
+MODULE_PARM_DESC(mjpeg_bpp, "MJPEG bits per pixel for bandwidth quirk");
 
 /* ------------------------------------------------------------------------
  * Driver initialization and cleanup
diff --git a/drivers/media/usb/uvc/uvc_video.c 
b/drivers/media/usb/uvc/uvc_video.c
index fb86d6a..382a0be 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -127,7 +127,8 @@ static void uvc_fixup_video_ctrl(struct uvc_streaming 
*stream,
        if ((ctrl->dwMaxPayloadTransferSize & 0xffff0000) == 0xffff0000)
                ctrl->dwMaxPayloadTransferSize &= ~0xffff0000;
 
-       if (!(format->flags & UVC_FMT_FLAG_COMPRESSED) &&
+       if ((!(format->flags & UVC_FMT_FLAG_COMPRESSED) ||
+                       (format->fcc == V4L2_PIX_FMT_MJPEG)) &&
            stream->dev->quirks & UVC_QUIRK_FIX_BANDWIDTH &&
            stream->intf->num_altsetting > 1) {
                u32 interval;
-- 
2.7.4