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From: Oleksandr Natalenko <oleksandr@natalenko.name>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
 Mauro Carvalho Chehab <mchehab@kernel.org>,
 Ricardo Ribalda <ribalda@chromium.org>
Cc: linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
 "hn.chen" <hn.chen@sunplusit.com>, Hans Verkuil <hverkuil@xs4all.nl>,
 Ricardo Ribalda <ribalda@chromium.org>,
 Sergey Senozhatsky <senozhatsky@chromium.org>
Subject:
 Re: [PATCH v10 3/6] media: uvcvideo: Quirk for invalid dev_sof in Logitech
 C922
Date: Sat, 23 Mar 2024 13:16:08 +0100
Message-ID: <2722561.mvXUDI8C0e@natalenko.name>
In-Reply-To: <20240323-resend-hwtimestamp-v10-3-b08e590d97c7@chromium.org>
References:
 <20240323-resend-hwtimestamp-v10-0-b08e590d97c7@chromium.org>
 <20240323-resend-hwtimestamp-v10-3-b08e590d97c7@chromium.org>
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From: Oleksandr Natalenko <oleksandr@natalenko.name>
Date: Sat, 23 Mar 2024 13:16:08 +0100
Message-ID: <2722561.mvXUDI8C0e@natalenko.name>
MIME-Version: 1.0

Hello.

On sobota 23. b=C5=99ezna 2024 11:48:04, CET Ricardo Ribalda wrote:
> Logitech C922 internal SOF does not increases at a stable rate of 1kHz.
> This causes that the device_sof and the host_sof run at different rates,
> breaking the clock domain conversion algorithm. Eg:
>=20
> 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

How do I check whether C920 (046d:082d) is affected too? I have got one, I =
can run tests on it as long as those will not blow the webcam up.

Thanks.

> 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.
>=20
> 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.
>=20
> 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
>=20
> This bug in the camera firmware has been confirmed by the vendor.
>=20
> lsusb -v
>=20
> 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
>=20
> Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> ---
>  drivers/media/usb/uvc/uvc_driver.c |  9 +++++++++
>  drivers/media/usb/uvc/uvc_video.c  | 11 +++++++++++
>  drivers/media/usb/uvc/uvcvideo.h   |  1 +
>  3 files changed, 21 insertions(+)
>=20
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/u=
vc_driver.c
> index bbd90123a4e76..723e6d5680c2e 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -2574,6 +2574,15 @@ static const struct usb_device_id uvc_ids[] =3D {
>  	  .bInterfaceSubClass	=3D 1,
>  	  .bInterfaceProtocol	=3D 0,
>  	  .driver_info		=3D UVC_INFO_QUIRK(UVC_QUIRK_RESTORE_CTRLS_ON_INIT) },
> +	/* Logitech HD Pro Webcam C922 */
> +	{ .match_flags		=3D USB_DEVICE_ID_MATCH_DEVICE
> +				| USB_DEVICE_ID_MATCH_INT_INFO,
> +	  .idVendor		=3D 0x046d,
> +	  .idProduct		=3D 0x085c,
> +	  .bInterfaceClass	=3D USB_CLASS_VIDEO,
> +	  .bInterfaceSubClass	=3D 1,
> +	  .bInterfaceProtocol	=3D 0,
> +	  .driver_info		=3D UVC_INFO_QUIRK(UVC_QUIRK_INVALID_DEVICE_SOF) },
>  	/* Chicony CNF7129 (Asus EEE 100HE) */
>  	{ .match_flags		=3D 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/uv=
c_video.c
> index b2e70fcf4eb4c..d6ca383f643e3 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -558,6 +558,17 @@ uvc_video_clock_decode(struct uvc_streaming *stream,=
 struct uvc_buffer *buf,
>  	stream->clock.last_sof =3D dev_sof;
> =20
>  	host_sof =3D 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.
> +	 * 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.
> +	 */
> +	if (stream->dev->quirks & UVC_QUIRK_INVALID_DEVICE_SOF)
> +		dev_sof =3D host_sof;
> +
>  	time =3D uvc_video_get_time();
> =20
>  	/*
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvc=
video.h
> index 6fb0a78b1b009..cb9dd50bba8ac 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
> =20
>  /* Format flags */
>  #define UVC_FMT_FLAG_COMPRESSED		0x00000001
>=20
>=20


=2D-=20
Oleksandr Natalenko (post-factum)
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