Hi,
2014-03-05 23:01 GMT+00:00 William Manley <will@xxxxxxxxxxxxxxxxx>:
> Hi All
>
> I've been attempting to use the Logitech C920 with the uvcvideo driver.
> I set the controls with v4l2-ctl but some of them change during
> VIDIOC_STREAMON. My understanding is that the values of controls should
> be preserved.
>
> Minimal test case:
>
> #include <linux/videodev2.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <fcntl.h>
> #include <errno.h>
> #include <string.h>
> #include <unistd.h>
> #include <sys/ioctl.h>
>
> #define DEVICE "/dev/video2"
>
> int main()
> {
> int fd, type;
>
> fd = open(DEVICE, O_RDWR | O_CLOEXEC);
> if (fd < 0) {
> perror("Failed to open " DEVICE "\n");
> return 1;
> }
>
> struct v4l2_requestbuffers reqbuf = {
> .type = V4L2_BUF_TYPE_VIDEO_CAPTURE,
> .memory = V4L2_MEMORY_MMAP,
> .count = 1,
> };
>
> if (-1 == ioctl (fd, VIDIOC_REQBUFS, &reqbuf)) {
> perror("VIDIOC_REQBUFS");
> return 1;
> }
>
> system("v4l2-ctl -d" DEVICE " -l | grep exposure_absolute");
>
> type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
> if (ioctl (fd, VIDIOC_STREAMON, &type) != 0) {
> perror("VIDIOC_STREAMON");
> return 1;
> }
>
> printf("VIDIOC_STREAMON\n");
>
> usleep(100000);
> system("v4l2-ctl -d" DEVICE " -l | grep exposure_absolute");
>
> return 0;
> }
>
> None of the other controls seem to be affected. Note: to get the C920
> to report exposure_absolute correctly I also had to make this change to
> the uvcvideo kernel driver:
>
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c
> b/drivers/media/usb/uvc/uvc_ctrl.c
> index a2f4501..e7c805b 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -227,7 +227,8 @@ static struct uvc_control_info uvc_ctrls[] = {
> .size = 4,
> .flags = UVC_CTRL_FLAG_SET_CUR
> | UVC_CTRL_FLAG_GET_RANGE
> - | UVC_CTRL_FLAG_RESTORE,
> + | UVC_CTRL_FLAG_RESTORE
> + | UVC_CTRL_FLAG_AUTO_UPDATE,
> },
> {
> .entity = UVC_GUID_UVC_CAMERA,
>
>
> The variables seem to be changed when the URBs are Submitted. To
> investigate I made the following change to the uvc driver:
>
>
> diff --git a/drivers/media/usb/uvc/uvc_video.c
> b/drivers/media/usb/uvc/uvc_video.c
> index 3394c34..f2f66f6 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -1649,17 +1649,23 @@ static int uvc_init_video(struct uvc_streaming
> *stream, gfp_t gfp_flags)
> if (ret < 0)
> return ret;
>
> + /* No effect: */
> + uvc_ctrl_resume_device(stream->dev);
> +
> /* Submit the URBs. */
> for (i = 0; i < UVC_URBS; ++i) {
> ret = usb_submit_urb(stream->urb[i], gfp_flags);
> if (ret < 0) {
> uvc_printk(KERN_ERR, "Failed to submit URB %u "
> "(%d).\n", i, ret);
> uvc_uninit_video(stream, 1);
> return ret;
> }
> }
>
> + /* "Fixes" the issue: */
> + uvc_ctrl_resume_device(stream->dev);
> +
> return 0;
> }
>
>
> At this point the backtrace looks something like:
>
> uvc_init_video
> uvc_video_enable
> uvc_v4l2_do_ioctl (in the case VIDIOC_STREAMON:)
>
> The call to uvc_ctrl_resume_device() has the effect that the v4l2 ctrls
> which are cached in the kernel get resubmitted to the camera as if it
> were coming out of suspend/resume.
>
> I've looked at the wireshark capture of USB traffic and I can't find
> anywhere where the host causes exposure_auto to change. The camera does
> have a mode where it would change by itself but that is disabled
> (exposure_auto=1).
This alone doesn't guarantee that exposure absolute is untouched.
To do so you need to set V4L2_CID_EXPOSURE_AUTO_PRIORITY to 0 and
V4L2_CID_EXPOSURE_AUTO to V4L2_EXPOSURE_MANUAL
> I've uploaded the wireshark trace to:
>
> http://williammanley.net/usb-wireshark-streamon.pcapng
>
> I'm guessing that this is a hardware bug. One fix would be modify the
> driver to save all values at the beginning of STREAMON and then restore
> them at the end. What do you think?
>
> Thanks
>
> Will
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Regards,
Paulo
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