Hi Ricardo, Thank you for the patch. On Wed, Mar 15, 2023 at 02:30:14PM +0100, Ricardo Ribalda wrote: > Logitech C922 internal SOF does not increases at a stable rate of 1kHz. The next thing you know they will redefine to value of pi to be 3. > This causes that the device_sof and the host_sof run at different rates, > breaking the clock domain conversion algorithm. Eg: > > 30 (6) [-] none 30 614400 B 21.245557 21.395214 34.133 fps ts mono/SoE > 31 (7) [-] none 31 614400 B 21.275327 21.427246 33.591 fps ts mono/SoE > 32 (0) [-] none 32 614400 B 21.304739 21.459256 34.000 fps ts mono/SoE > 33 (1) [-] none 33 614400 B 21.334324 21.495274 33.801 fps ts mono/SoE > * 34 (2) [-] none 34 614400 B 21.529237 21.527297 5.130 fps ts mono/SoE > * 35 (3) [-] none 35 614400 B 21.649416 21.559306 8.321 fps ts mono/SoE > 36 (4) [-] none 36 614400 B 21.678789 21.595320 34.045 fps ts mono/SoE > ... > 99 (3) [-] none 99 614400 B 23.542226 23.696352 33.541 fps ts mono/SoE > 100 (4) [-] none 100 614400 B 23.571578 23.728404 34.069 fps ts mono/SoE > 101 (5) [-] none 101 614400 B 23.601425 23.760420 33.504 fps ts mono/SoE > * 102 (6) [-] none 102 614400 B 23.798324 23.796428 5.079 fps ts mono/SoE > * 103 (7) [-] none 103 614400 B 23.916271 23.828450 8.478 fps ts mono/SoE > 104 (0) [-] none 104 614400 B 23.945720 23.860479 33.957 fps ts mono/SoE > > Instead of disabling completely the hardware timestamping for such > hardware we take the assumption that the packet handling jitter is > under 2ms and use the host_sof as dev_sof. > > We can think of the UVC hardware clock as a system with a coarse clock > (the SOF) and a fine clock (the PTS). The coarse clock can be replaced > with a clock on the same frequency, if the jitter of such clock is > smaller than its sampling rate. That way we can save some of the > precision of the fine clock. > > To probe this point we have run three experiments on the Logitech C922. > On that experiment we run the camera at 33fps and we analyse the > difference in msec between a frame and its predecessor. If we display > the histogram of that value, a thinner histogram will mean a better > meassurement. The results for: > - original hw timestamp: https://ibb.co/D1HJJ4x > - pure software timestamp: https://ibb.co/QC9MgVK > - modified hw timestamp: https://ibb.co/8s9dBdk > > This bug in the camera firmware has been confirmed by the vendor. > > lsusb -v > > Bus 001 Device 044: ID 046d:085c Logitech, Inc. C922 Pro Stream Webcam > Device Descriptor: > bLength 18 > bDescriptorType 1 > bcdUSB 2.00 > bDeviceClass 239 Miscellaneous Device > bDeviceSubClass 2 > bDeviceProtocol 1 Interface Association > bMaxPacketSize0 64 > idVendor 0x046d Logitech, Inc. > idProduct 0x085c C922 Pro Stream Webcam > bcdDevice 0.16 > iManufacturer 0 > iProduct 2 C922 Pro Stream Webcam > iSerial 1 80B912DF > bNumConfigurations 1 > > Reviewed-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> > Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx> > --- > drivers/media/usb/uvc/uvc_driver.c | 9 +++++++++ > drivers/media/usb/uvc/uvc_video.c | 8 ++++++++ > drivers/media/usb/uvc/uvcvideo.h | 1 + > 3 files changed, 18 insertions(+) > > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c > index 7aefa76a42b3..678a5736c9df 100644 > --- a/drivers/media/usb/uvc/uvc_driver.c > +++ b/drivers/media/usb/uvc/uvc_driver.c > @@ -2549,6 +2549,15 @@ static const struct usb_device_id uvc_ids[] = { > .bInterfaceSubClass = 1, > .bInterfaceProtocol = 0, > .driver_info = UVC_INFO_QUIRK(UVC_QUIRK_RESTORE_CTRLS_ON_INIT) }, > + /* Logitech HD Pro Webcam C922 */ > + { .match_flags = USB_DEVICE_ID_MATCH_DEVICE > + | USB_DEVICE_ID_MATCH_INT_INFO, > + .idVendor = 0x046d, > + .idProduct = 0x085c, > + .bInterfaceClass = USB_CLASS_VIDEO, > + .bInterfaceSubClass = 1, > + .bInterfaceProtocol = 0, > + .driver_info = UVC_INFO_QUIRK(UVC_QUIRK_INVALID_DEVICE_SOF) }, > /* Chicony CNF7129 (Asus EEE 100HE) */ > { .match_flags = USB_DEVICE_ID_MATCH_DEVICE > | USB_DEVICE_ID_MATCH_INT_INFO, > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c > index 1f416c494acc..4d566edb73e7 100644 > --- a/drivers/media/usb/uvc/uvc_video.c > +++ b/drivers/media/usb/uvc/uvc_video.c > @@ -547,6 +547,14 @@ uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf, > stream->clock.last_sof = dev_sof; > > host_sof = usb_get_current_frame_number(stream->dev->udev); > + > + /* > + * On some devices, like the Logitech C922, the device SOF does not run > + * at a stable rate of 1kHz. For those devices use the host SOF instead. I'm still not very convinced, as without a formal proof I think there's some luck involved, and it may break later. This being said, given that this is gated by a quirk, it won't impact other devices, and we can deal with regressions when they happen. Could we record it here: * On some devices, like the Logitech C922, the device SOF does not run * at a stable rate of 1kHz. For those devices use the host SOF instead. * This improves the timestamp precision in the tests performed so far, * even if the exact reason hasn't been fully determined. or something along those lines ? Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > + */ > + if (stream->dev->quirks & UVC_QUIRK_INVALID_DEVICE_SOF) > + dev_sof = host_sof; > + > time = uvc_video_get_time(); > > /* > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h > index 9a596c8d894a..07b2fdb80adf 100644 > --- a/drivers/media/usb/uvc/uvcvideo.h > +++ b/drivers/media/usb/uvc/uvcvideo.h > @@ -73,6 +73,7 @@ > #define UVC_QUIRK_FORCE_Y8 0x00000800 > #define UVC_QUIRK_FORCE_BPP 0x00001000 > #define UVC_QUIRK_WAKE_AUTOSUSPEND 0x00002000 > +#define UVC_QUIRK_INVALID_DEVICE_SOF 0x00004000 > > /* Format flags */ > #define UVC_FMT_FLAG_COMPRESSED 0x00000001 > -- Regards, Laurent Pinchart
