From 76799be6eb56e7f95d2d6aeebab7c7ec94b12f85 Mon Sep 17 00:00:00 2001 From: Jacopo Mondi Date: Mon, 7 Jul 2025 17:55:35 +0200 Subject: [PATCH] media: Documentation: kapi: Add v4l2 generic ISP support Add to the driver-api documentation the v4l2-isp.h types and helpers documentation. Reviewed-by: Daniel Scally Reviewed-by: Michael Riesch Acked-by: Sakari Ailus Reviewed-by: Laurent Pinchart Tested-by: Lad Prabhakar Signed-off-by: Jacopo Mondi Signed-off-by: Hans Verkuil --- Documentation/driver-api/media/v4l2-core.rst | 1 + Documentation/driver-api/media/v4l2-isp.rst | 49 ++++++++++++++++++++ MAINTAINERS | 1 + 3 files changed, 51 insertions(+) create mode 100644 Documentation/driver-api/media/v4l2-isp.rst diff --git a/Documentation/driver-api/media/v4l2-core.rst b/Documentation/driver-api/media/v4l2-core.rst index ad987c34ad2a8..a5f5102c64cca 100644 --- a/Documentation/driver-api/media/v4l2-core.rst +++ b/Documentation/driver-api/media/v4l2-core.rst @@ -27,3 +27,4 @@ Video4Linux devices v4l2-common v4l2-tveeprom v4l2-jpeg + v4l2-isp diff --git a/Documentation/driver-api/media/v4l2-isp.rst b/Documentation/driver-api/media/v4l2-isp.rst new file mode 100644 index 0000000000000..618ae614ff794 --- /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 diff --git a/MAINTAINERS b/MAINTAINERS index e4c8b2d533bdc..ebe6e75b1a2f5 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -26889,6 +26889,7 @@ V4L2 GENERIC ISP PARAMETERS AND STATISTIC FORMATS M: Jacopo Mondi L: linux-media@vger.kernel.org S: Maintained +F: Documentation/driver-api/media/v4l2-isp.rst F: Documentation/userspace-api/media/v4l/v4l2-isp.rst F: drivers/media/v4l2-core/v4l2-isp.c F: include/media/v4l2-isp.h -- 2.47.3