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Date: Fri, 22 Mar 2024 09:32:56 +0100
From: Ricardo Ribalda <ribalda@...omium.org>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>, Sergey Senozhatsky <senozhatsky@...omium.org>,
linux-kernel@...r.kernel.org, "hn.chen" <hn.chen@...plusit.com>,
linux-media@...r.kernel.org
Subject: Re: [PATCH v9 3/6] media: uvcvideo: Quirk for invalid dev_sof in
Logitech C922
Hi Laurent
On Fri, 22 Mar 2024 at 00:44, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> 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@...omium.org>
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > ---
> > 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 ?
How does this sound:
/*
* 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.
+ * In the tests performed so far, this improves the timestamp precision.
+ * This is probably explained by a small packet handling jitter from the
+ * host, but the exact reason hasn't been fully determined.
*/
>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>
> > + */
> > + 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
--
Ricardo Ribalda
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