* Re: [PATCH v3] media: uvcvideo: Handle payloads starting in the middle of a bulk URB
2026-11-02 22:03 ` [PATCH v3] media: uvcvideo: Handle payloads starting in the middle of a bulk URB Muhammad Waleed Badar
@ 2026-11-02 22:31 ` Laurent Pinchart
0 siblings, 0 replies; 2+ messages in thread
From: Laurent Pinchart @ 2026-11-02 22:31 UTC (permalink / raw)
To: Muhammad Waleed Badar
Cc: linux-media, Hans de Goede, Muhammad Waleed Badar,
Ricardo Ribalda, Mauro Carvalho Chehab, linux-kernel
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On Tue, 03 Nov 2026 03:03:36 +0500, Muhammad Waleed Badar <walid.badar@gmail.com> wrote:
> The bulk decoder assumes that every payload starts at the beginning of
> a URB. It detects the end of a payload either by a short URB or by the
> accumulated payload size reaching dwMaxPayloadTransferSize, and then
> decodes the start of the next URB as a new payload header.
>
> The Realtek USB Camera (0bda:579f) integrated in Razer Blade laptops
> sends payloads of dwMaxPayloadTransferSize bytes back to back without
> aligning them to URB boundaries, which is not compliant with the UVC
> specification. When a frame spans more than one payload, the next
> payload header lands in the middle of a URB. The driver then copies
> that header and the data that follows into the current frame, and
> parses frame data at the start of the next URB as a header. This shows
> up as "Marking buffer as bad (error bit set)" and "Dropping payload
> (out of sync)" trace messages, and most frames larger than one payload
> are returned empty or truncated. On this camera every MJPEG mode above
> 1280x720 is affected.
>
> Add a UVC_QUIRK_BULK_UNALIGNED_PAYLOAD quirk for this device. When it
> is set and a payload ends in the middle of a URB, split the URB at the
> payload boundary and decode the remainder as a new payload, provided
> that it looks like a payload header (EOH bit set and a header length
> that fits the data and covers the announced PTS and SCR fields).
> Otherwise the URB is processed as before. Print a non compliance
> warning once when the workaround is used.
>
> The quirk is limited to this device, and the header check is kept as a
> safeguard, because other non compliant bulk devices append trailer
> data to their payloads, and decoding that data as a payload header
> would break them. Devices without the quirk are unaffected. The quirk
> can be enabled for other devices with the quirks module parameter.
>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=207045
> Assisted-by: Claude:claude-opus-5.5
> Signed-off-by: Muhammad Waleed Badar <walid.badar@gmail.com>
> ---
> Changes in v3:
> - Align the continuation line of the uvc_video_decode_bulk() declaration
> with the open parenthesis, as reported by the Media CI checkpatch run.
> - Link to v2: https://lore.kernel.org/r/20261025170220.42789-1-walid.badar@gmail.com
>
> Changes in v2:
> - Limit the workaround to the Realtek 0bda:579f camera through a new
> UVC_QUIRK_BULK_UNALIGNED_PAYLOAD quirk (Hans de Goede).
> - Only split a URB when the remainder looks like a valid payload header,
> so devices that append trailer data are not affected, and print a
> non-compliance warning once (Ricardo Ribalda).
> - Link to v1: https://lore.kernel.org/r/20261009165248.56440-1-walid.badar@gmail.com
>
> drivers/media/usb/uvc/uvc_driver.c | 9 +++
> drivers/media/usb/uvc/uvc_video.c | 95 +++++++++++++++++++++++++-----
> drivers/media/usb/uvc/uvcvideo.h | 2 +
> 3 files changed, 90 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> index e289cc71b..cfdcfd96a 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -2887,6 +2887,15 @@ static const struct usb_device_id uvc_ids[] = {
> .bInterfaceSubClass = 1,
> .bInterfaceProtocol = 0,
> .driver_info = (kernel_ulong_t)&uvc_quirk_probe_minmax },
> + /* Realtek USB Camera (Razer Blade) */
> + { .match_flags = USB_DEVICE_ID_MATCH_DEVICE
> + | USB_DEVICE_ID_MATCH_INT_INFO,
> + .idVendor = 0x0bda,
> + .idProduct = 0x579f,
> + .bInterfaceClass = USB_CLASS_VIDEO,
> + .bInterfaceSubClass = 1,
> + .bInterfaceProtocol = 0,
> + .driver_info = UVC_INFO_QUIRK(UVC_QUIRK_BULK_UNALIGNED_PAYLOAD) },
> /* Sonix Technology Co. Ltd. - 292A IPC AR0330 */
> { .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 fc3536a43..8a1e4bc77 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -1612,27 +1612,20 @@ static void uvc_video_decode_isoc(struct uvc_urb *uvc_urb,
> }
> }
>
> -static void uvc_video_decode_bulk(struct uvc_urb *uvc_urb,
> - struct uvc_buffer *buf, struct uvc_buffer *meta_buf)
> +static void uvc_video_decode_bulk_chunk(struct uvc_urb *uvc_urb,
> + struct uvc_buffer **bufp,
> + struct uvc_buffer **meta_bufp,
> + u8 *mem, int len, bool short_urb)
> {
> - struct urb *urb = uvc_urb->urb;
> struct uvc_streaming *stream = uvc_urb->stream;
> - u8 *mem;
> - int len, ret;
> -
> - /*
> - * Ignore ZLPs if they're not part of a frame, otherwise process them
> - * to trigger the end of payload detection.
> - */
> - if (urb->actual_length == 0 && stream->bulk.header_size == 0)
> - return;
> + struct uvc_buffer *buf = *bufp;
> + struct uvc_buffer *meta_buf = *meta_bufp;
> + int ret;
>
> - mem = urb->transfer_buffer;
> - len = urb->actual_length;
> stream->bulk.payload_size += len;
>
> /*
> - * If the URB is the first of its payload, decode and save the
> + * If the chunk is the first of its payload, decode and save the
> * header.
> */
> if (stream->bulk.header_size == 0 && !stream->bulk.skip_payload) {
> @@ -1671,7 +1664,7 @@ static void uvc_video_decode_bulk(struct uvc_urb *uvc_urb,
> * Detect the payload end by a URB smaller than the maximum size (or
> * a payload size equal to the maximum) and process the header again.
> */
> - if (urb->actual_length < urb->transfer_buffer_length ||
> + if (short_urb ||
> stream->bulk.payload_size >= stream->bulk.max_payload_size) {
> if (!stream->bulk.skip_payload && buf != NULL) {
> uvc_video_decode_end(stream, buf, stream->bulk.header,
> @@ -1684,6 +1677,76 @@ static void uvc_video_decode_bulk(struct uvc_urb *uvc_urb,
> stream->bulk.skip_payload = 0;
> stream->bulk.payload_size = 0;
> }
> +
> + *bufp = buf;
> + *meta_bufp = meta_buf;
> +}
> +
> +/*
> + * Check whether data looks like the start of a payload: a header with the
> + * EOH bit set, and a length that fits in the data and is large enough for
> + * the PTS and SCR fields it announces.
> + */
> +static bool uvc_video_bulk_is_header(const u8 *data, int len)
> +{
> + unsigned int min_len = 2;
> +
> + if (len < 2 || !(data[1] & UVC_STREAM_EOH))
> + return false;
> +
> + if (data[1] & UVC_STREAM_PTS)
> + min_len += 4;
> + if (data[1] & UVC_STREAM_SCR)
> + min_len += 6;
> +
> + return data[0] >= min_len && data[0] <= len;
> +}
> +
> +static void uvc_video_decode_bulk(struct uvc_urb *uvc_urb,
> + struct uvc_buffer *buf, struct uvc_buffer *meta_buf)
> +{
> + struct urb *urb = uvc_urb->urb;
> + struct uvc_streaming *stream = uvc_urb->stream;
> + bool short_urb = urb->actual_length < urb->transfer_buffer_length;
> + u8 *mem;
> + int len;
> +
> + /*
> + * Ignore ZLPs if they're not part of a frame, otherwise process them
> + * to trigger the end of payload detection.
> + */
> + if (urb->actual_length == 0 && stream->bulk.header_size == 0)
> + return;
> +
> + mem = urb->transfer_buffer;
> + len = urb->actual_length;
> +
> + do {
> + int chunk = len;
> + int rem = stream->bulk.max_payload_size -
> + stream->bulk.payload_size;
> +
> + /*
> + * Some devices (such as the Realtek 0bda:579f) start the next
> + * payload immediately after the previous one instead of in a
> + * new URB, so a payload boundary can fall in the middle of a
> + * URB. For those, split the URB at the payload boundary if
> + * the data that follows looks like a payload header. Other
> + * devices may append trailer data to a payload, which must
> + * not be decoded as a header, so leave them alone.
> + */
> + if ((stream->dev->quirks & UVC_QUIRK_BULK_UNALIGNED_PAYLOAD) &&
> + len > rem && uvc_video_bulk_is_header(mem + rem, len - rem)) {
> + uvc_warn_once(stream->dev, UVC_WARN_BULK_UNALIGNED,
> + "UVC non compliance - bulk payload starts in the middle of a URB. Enabling workaround.\n");
> + chunk = rem;
> + }
> +
> + uvc_video_decode_bulk_chunk(uvc_urb, &buf, &meta_buf, mem,
> + chunk, short_urb && chunk == len);
> + mem += chunk;
> + len -= chunk;
> + } while (len > 0);
> }
>
> static void uvc_video_encode_bulk(struct uvc_urb *uvc_urb,
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index b6bcee4a2..59ad516ae 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -81,6 +81,7 @@
> #define UVC_QUIRK_INVALID_DEVICE_SOF 0x00010000
> #define UVC_QUIRK_MJPEG_NO_EOF 0x00020000
> #define UVC_QUIRK_MSXU_META 0x00040000
> +#define UVC_QUIRK_BULK_UNALIGNED_PAYLOAD 0x00080000
>
> /* Format flags */
> #define UVC_FMT_FLAG_COMPRESSED 0x00000001
> @@ -661,6 +662,7 @@ static inline struct uvc_fh *to_uvc_fh(struct file *filp)
> #define UVC_WARN_MINMAX 0
> #define UVC_WARN_PROBE_DEF 1
> #define UVC_WARN_XU_GET_RES 2
> +#define UVC_WARN_BULK_UNALIGNED 3
>
> extern unsigned int uvc_clock_param;
> extern unsigned int uvc_no_drop_param;
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