Hi Ricardo,
Thank you for the patch.
On Wed, Mar 15, 2023 at 02:30:13PM +0100, Ricardo Ribalda wrote:
> Some SunplusIT cameras took a borderline interpretation of the UVC 1.5
> standard, and fill the PTS and SCR fields with invalid data if the
> package does not contain data.
>
> "STC must be captured when the first video data of a video frame is put
> on the USB bus."
>
> Eg:
"Some SunplusIT devices send, e.g.,"
>
> buffer: 0xa7755c00 len 000012 header:0x8c stc 00000000 sof 0000 pts 00000000
> buffer: 0xa7755c00 len 000012 header:0x8c stc 00000000 sof 0000 pts 00000000
> buffer: 0xa7755c00 len 000668 header:0x8c stc 73779dba sof 070c pts 7376d37a
"while the UVC specification meant that the first two packets shouldn't
have had the SCR bit set in the header."
>
> This borderline/buggy interpretation has been implemented in a variety
> of devices, from directly SunplusIT and from other OEMs that rebrand
> SunplusIT products. So quirking based on VID:PID will be problematic.
>
> All the affected modules have the following extension unit:
> VideoControl Interface Descriptor:
> guidExtensionCode {82066163-7050-ab49-b8cc-b3855e8d221d}
>
> But the vendor plans to use that GUID in the future and fix the bug,
> this means that we should use heuristic to figure out the broken
> packets.
Because it would have been too easy otherwise of course :-)
>
> This patch takes care of this.
>
> lsusb of one of the affected cameras:
>
> Bus 001 Device 003: ID 1bcf:2a01 Sunplus Innovation Technology Inc.
> Device Descriptor:
> bLength 18
> bDescriptorType 1
> bcdUSB 2.01
> bDeviceClass 239 Miscellaneous Device
> bDeviceSubClass 2 ?
> bDeviceProtocol 1 Interface Association
> bMaxPacketSize0 64
> idVendor 0x1bcf Sunplus Innovation Technology Inc.
> idProduct 0x2a01
> bcdDevice 0.02
> iManufacturer 1 SunplusIT Inc
> iProduct 2 HanChen Wise Camera
> iSerial 3 01.00.00
> bNumConfigurations 1
>
> Tested-by: HungNien Chen <hn.chen@xxxxxxxxxxxxx>
> Reviewed-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
> Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> ---
> drivers/media/usb/uvc/uvc_video.c | 20 +++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> index 4ff4ab4471fe..1f416c494acc 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -478,6 +478,7 @@ uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf,
> ktime_t time;
> u16 host_sof;
> u16 dev_sof;
> + u32 dev_stc;
>
> switch (data[1] & (UVC_STREAM_PTS | UVC_STREAM_SCR)) {
> case UVC_STREAM_PTS | UVC_STREAM_SCR:
> @@ -526,6 +527,23 @@ uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf,
> if (dev_sof == stream->clock.last_sof)
> return;
>
> + dev_stc = get_unaligned_le32(&data[header_size - 6]);
> +
> + /*
> + * STC (Source Time Clock) is the clock used by the camera. The UVC 1.5
> + * standard states that it "must be captured when the first video data
> + * of a video frame is put on the USB bus".
> + * Most of the vendors, clear the `UVC_STREAM_SCR` bit when the data is
> + * not valid, other vendors always set the `UVC_STREAM_SCR` bit and
> + * expect that the driver only samples the stc if there is data on the
> + * packet.
> + * Ignore all the hardware timestamp information if there is no data
> + * and stc and sof are zero.
> + */
I'd like to expand this a bit (partly to make sure I understand the
issue correctly):
/*
* STC (Source Time Clock) is the clock used by the camera. The UVC 1.5
* standard states that it "must be captured when the first video data
* of a video frame is put on the USB bus". This is generally understood
* as requiring devices to clear the payload header's SCR bit before
* the first packet containing video data.
*
* Most vendors follow that interpretation, but some (namely SunplusIT)
* always set the `UVC_STREAM_SCR` bit, fill the SCR field with 0's,
* and expect that the driver only processes the SCR if there is data in
* the packet.
*
* Ignore all the hardware timestamp information if we haven't received
* any data for this frame yet, the packet contains no data, and both
* STC and SOF are zero. This heuristics should be safe on compliant
* devices. This should be safe with compliant devices, as in the very
* unlikely case where a UVC 1.1 device would send timing information
* only before the first packet containing data, and both STC and SOF
* happen to be zero for a particular frame, we would only miss one
* clock sample and the clock recovery algorithm wouldn't suffer from
* this condition.
*/
Is this correct (and fine with you) ? If so,
Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> + if (buf && buf->bytesused == 0 && len == header_size &&
> + dev_stc == 0 && dev_sof == 0)
> + return;
> +
> stream->clock.last_sof = dev_sof;
>
> host_sof = usb_get_current_frame_number(stream->dev->udev);
> @@ -564,7 +582,7 @@ uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf,
> spin_lock_irqsave(&stream->clock.lock, flags);
>
> sample = &stream->clock.samples[stream->clock.head];
> - sample->dev_stc = get_unaligned_le32(&data[header_size - 6]);
> + sample->dev_stc = dev_stc;
> sample->dev_sof = dev_sof;
> sample->host_sof = host_sof;
> sample->host_time = time;
>
--
Regards,
Laurent Pinchart
