Re: [PATCH v2] media: uvcvideo: Quirk for hardware with invalid sof
From: Ricardo Ribalda
Date: Thu Aug 19 2021 - 02:48:09 EST
Hi Laurent
Thanks for your prompt reply
On Thu, 19 Aug 2021 at 00:22, Laurent Pinchart
<laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
>
> Hi Ricardo,
>
> Thank you for the patch.
>
> On Wed, Aug 18, 2021 at 10:35:02PM +0200, Ricardo Ribalda wrote:
> > The hardware timestamping code has the assumption than the device_sof
> > and the host_sof run at the same frequency (1 KHz).
> >
> > Unfortunately, this is not the case for all the hardware. Add a quirk to
> > support such hardware.
> >
> > Note on how to identify such hardware:
> > When running with "yavta -c /dev/videoX" Look for periodic jumps of the
> > fps. 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
> >
> > They happen because the delta_sof calculated at
> > uvc_video_clock_host_sof(), wraps periodically, as both clocks drift.
>
> That looks plain wrong. First of all, the whole purpose of the SOF clock
> is to have a shared clock between the host and the device. It makes no
> sense for a device to have a free-running "SOF" clock. Given the log
> above, the issue occurs so quickly that it doesn't seem to be a mere
> drift of a free running clock. Could you investigate this more carefully
> ?
In my test the dev_sof runs at 887.91Hz and the dev_sof at 1000.35Hz.
If I plot the difference of both clocks host_sof - (dev_sof % 2048), I
get this nice graph
https://imgur.com/a/5fQnKa7
I agree that it makes not sense to have a free-running "SOF", but the
manufacturer thinks otherwise :)
Best regards
>
> > Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> > ---
> > v2: Fix typo in frequency
> >
> > drivers/media/usb/uvc/uvc_driver.c | 9 +++++++++
> > drivers/media/usb/uvc/uvc_video.c | 11 +++++++++--
> > drivers/media/usb/uvc/uvcvideo.h | 2 ++
> > 3 files changed, 20 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> > index 9a791d8ef200..d1e6cba10b15 100644
> > --- a/drivers/media/usb/uvc/uvc_driver.c
> > +++ b/drivers/media/usb/uvc/uvc_driver.c
> > @@ -2771,6 +2771,15 @@ 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 6d0e474671a2..760ab015cf9c 100644
> > --- a/drivers/media/usb/uvc/uvc_video.c
> > +++ b/drivers/media/usb/uvc/uvc_video.c
> > @@ -518,13 +518,20 @@ uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf,
> > /* To limit the amount of data, drop SCRs with an SOF identical to the
> > * previous one.
> > */
> > - dev_sof = get_unaligned_le16(&data[header_size - 2]);
> > + if (stream->dev->quirks & UVC_QUIRK_INVALID_DEVICE_SOF)
> > + dev_sof = usb_get_current_frame_number(stream->dev->udev);
> > + else
> > + dev_sof = get_unaligned_le16(&data[header_size - 2]);
> > +
> > if (dev_sof == stream->clock.last_sof)
> > return;
> >
> > stream->clock.last_sof = dev_sof;
> >
> > - host_sof = usb_get_current_frame_number(stream->dev->udev);
> > + if (stream->dev->quirks & UVC_QUIRK_INVALID_DEVICE_SOF)
> > + host_sof = dev_sof;
> > + else
> > + host_sof = usb_get_current_frame_number(stream->dev->udev);
> > time = uvc_video_get_time();
> >
> > /* The UVC specification allows device implementations that can't obtain
> > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > index cce5e38133cd..89d909661915 100644
> > --- a/drivers/media/usb/uvc/uvcvideo.h
> > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > @@ -209,6 +209,8 @@
> > #define UVC_QUIRK_RESTORE_CTRLS_ON_INIT 0x00000400
> > #define UVC_QUIRK_FORCE_Y8 0x00000800
> > #define UVC_QUIRK_FORCE_BPP 0x00001000
> > +#define UVC_QUIRK_INVALID_DEVICE_SOF 0x00002000
> > +
> >
> > /* Format flags */
> > #define UVC_FMT_FLAG_COMPRESSED 0x00000001
>
> --
> Regards,
>
> Laurent Pinchart
--
Ricardo Ribalda