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e1ad270275
The documentation currently describes the UVC length field as the "length of the rest of the block", which can be misleading. The driver limits the data copied to a maximum of 12 bytes. This change adds a clarifying sentence to the documentation to make this restriction explicit. Reviewed-by: Hans de Goede <hansg@kernel.org> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org> Link: https://lore.kernel.org/r/20250707-uvc-meta-v8-2-ed17f8b1218b@chromium.org Signed-off-by: Hans de Goede <hansg@kernel.org> Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
54 lines
2.1 KiB
ReStructuredText
54 lines
2.1 KiB
ReStructuredText
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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.. _v4l2-meta-fmt-uvc:
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*******************************
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V4L2_META_FMT_UVC ('UVCH')
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*******************************
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UVC Payload Header Data
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Description
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===========
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This format describes standard UVC metadata, extracted from UVC packet headers
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and provided by the UVC driver through metadata video nodes. That data includes
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exact copies of the standard part of UVC Payload Header contents and auxiliary
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timing information, required for precise interpretation of timestamps, contained
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in those headers. See section "2.4.3.3 Video and Still Image Payload Headers" of
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the "UVC 1.5 Class specification" for details.
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Each UVC payload header can be between 2 and 12 bytes large. Buffers can
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contain multiple headers, if multiple such headers have been transmitted by the
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camera for the respective frame. However, the driver may drop headers when the
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buffer is full, when they contain no useful information (e.g. those without the
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SCR field or with that field identical to the previous header), or generally to
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perform rate limiting when the device sends a large number of headers.
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Each individual block contains the following fields:
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.. flat-table:: UVC Metadata Block
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:widths: 1 4
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:header-rows: 1
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:stub-columns: 0
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* - Field
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- Description
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* - __u64 ts;
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- system timestamp in host byte order, measured by the driver upon
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reception of the payload
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* - __u16 sof;
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- USB Frame Number in host byte order, also obtained by the driver as
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close as possible to the above timestamp to enable correlation between
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them
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* - :cspan:`1` *The rest is an exact copy of the UVC payload header:*
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* - __u8 length;
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- length of the rest of the block, including this field. Please note that
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regardless of this value, for V4L2_META_FMT_UVC the kernel will never
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copy more than 2-12 bytes.
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* - __u8 flags;
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- Flags, indicating presence of other standard UVC fields
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* - __u8 buf[];
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- The rest of the header, possibly including UVC PTS and SCR fields
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