Greg Kroah-Hartman
598cf27219
Link: https://lore.kernel.org/r/20260217200002.683975158@linuxfoundation.org Tested-by: Florian Fainelli <florian.fainelli@broadcom.com> Tested-by: Takeshi Ogasawara <takeshi.ogasawara@futuring-girl.com> Tested-by: Peter Schneider <pschneider1968@googlemail.com> Tested-by: Jon Hunter <jonathanh@nvidia.com> Tested-by: Salvatore Bonaccorso <carnil@debian.org> Tested-by: Brett A C Sheffield <bacs@librecast.net> Tested-by: Mark Brown <broonie@kernel.org> Tested-by: Luna Jernberg <droidbittin@gmail.com> Tested-by: Ronald Warsow <rwarsow@gmx.de> Tested-by: Justin M. Forbes <jforbes@fedoraproject.org> Tested-by: Ron Economos <re@w6rz.net> Tested-by: Miguel Ojeda <ojeda@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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2.1 KiB
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50 lines
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.. SPDX-License-Identifier: GPL-2.0
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V4L2 generic ISP parameters and statistics support
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Design rationale
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================
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ISP configuration parameters and statistics are processed and collected by
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drivers and exchanged with userspace through data types that usually
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reflect the ISP peripheral registers layout.
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Each ISP driver defines its own metadata output format for parameters and
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a metadata capture format for statistics. The buffer layout is realized by a
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set of C structures that reflects the registers layout. The number and types
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of C structures is fixed by the format definition and becomes part of the Linux
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kernel uAPI/uABI interface.
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Because of the hard requirement of backward compatibility when extending the
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user API/ABI interface, modifying an ISP driver capture or output metadata
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format after it has been accepted by mainline is very hard if not impossible.
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It generally happens, in fact, that after the first accepted revision of an ISP
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driver the buffers layout need to be modified, either to support new hardware
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blocks, to fix bugs or to support different revisions of the hardware.
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Each of these situations would require defining a new metadata format, making it
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really hard to maintain and extend drivers and requiring userspace to use
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the correct format depending on the kernel revision in use.
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V4L2 ISP configuration parameters
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=================================
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For these reasons, Video4Linux2 defines generic types for ISP configuration
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parameters and statistics. Drivers are still expected to define their own
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formats for their metadata output and capture nodes, but the buffers layout can
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be defined using the extensible and versioned types defined by
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include/uapi/linux/media/v4l2-isp.h.
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Drivers are expected to provide the definitions of their supported ISP blocks
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and the expected maximum size of a buffer.
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For driver developers a set of helper functions to assist them with validation
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of the buffer received from userspace is available in
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drivers/media/v4l2-core/v4l2-isp.c
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V4L2 ISP support driver documentation
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=====================================
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.. kernel-doc:: include/media/v4l2-isp.h
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