Documentation/driver-api/media/v4l2-isp.rst - linux/kernel/git/dhowells/linux-fs - Git at Google


            
            .. 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
	.. 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