Re: [PATCH v9 2/6] media: uvcvideo: Ignore empty TS packets
From: Ricardo Ribalda
Date: Fri Mar 22 2024 - 04:23:10 EST
Hi Laurent
Hi, I added some minor modifications, hope that it is fine with you.
Thanks!!
On Fri, 22 Mar 2024 at 00:26, Laurent Pinchart
<laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
>
> 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)
namely SunplusIT on some devices
> * 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
one clock sample from many
> * 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
--
Ricardo Ribalda