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Diffstat (limited to 'Documentation/driver-api/media/v4l2-isp.rst')
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diff --git a/Documentation/driver-api/media/v4l2-isp.rst b/Documentation/driver-api/media/v4l2-isp.rst new file mode 100644 index 000000000000..618ae614ff79 --- /dev/null +++ b/Documentation/driver-api/media/v4l2-isp.rst @@ -0,0 +1,49 @@ +.. SPDX-License-Identifier: GPL-2.0 + +V4L2 generic ISP parameters and statistics support +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Design rationale +================ + +ISP configuration parameters and statistics are processed and collected by +drivers and exchanged with userspace through data types that usually +reflect the ISP peripheral registers layout. + +Each ISP driver defines its own metadata output format for parameters and +a metadata capture format for statistics. The buffer layout is realized by a +set of C structures that reflects the registers layout. The number and types +of C structures is fixed by the format definition and becomes part of the Linux +kernel uAPI/uABI interface. + +Because of the hard requirement of backward compatibility when extending the +user API/ABI interface, modifying an ISP driver capture or output metadata +format after it has been accepted by mainline is very hard if not impossible. + +It generally happens, in fact, that after the first accepted revision of an ISP +driver the buffers layout need to be modified, either to support new hardware +blocks, to fix bugs or to support different revisions of the hardware. + +Each of these situations would require defining a new metadata format, making it +really hard to maintain and extend drivers and requiring userspace to use +the correct format depending on the kernel revision in use. + +V4L2 ISP configuration parameters +================================= + +For these reasons, Video4Linux2 defines generic types for ISP configuration +parameters and statistics. Drivers are still expected to define their own +formats for their metadata output and capture nodes, but the buffers layout can +be defined using the extensible and versioned types defined by +include/uapi/linux/media/v4l2-isp.h. + +Drivers are expected to provide the definitions of their supported ISP blocks +and the expected maximum size of a buffer. + +For driver developers a set of helper functions to assist them with validation +of the buffer received from userspace is available in +drivers/media/v4l2-core/v4l2-isp.c + +V4L2 ISP support driver documentation +===================================== +.. kernel-doc:: include/media/v4l2-isp.h |