On 27/09/2022 08:59, Sakari Ailus wrote:
Moi,
On Wed, Aug 31, 2022 at 05:13:42PM +0300, Tomi Valkeinen wrote:
From: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx>
Add documentation for VIDIOC_SUBDEV_G/S_ROUTING ioctl and add
description of multiplexed media pads and internal routing to the
V4L2-subdev documentation section.
Signed-off-by: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
---
.../userspace-api/media/v4l/dev-subdev.rst | 2 +
.../userspace-api/media/v4l/user-func.rst | 1 +
.../media/v4l/vidioc-subdev-g-routing.rst | 150 ++++++++++++++++++
3 files changed, 153 insertions(+)
create mode 100644 Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst
diff --git a/Documentation/userspace-api/media/v4l/dev-subdev.rst b/Documentation/userspace-api/media/v4l/dev-subdev.rst
index fd1de0a73a9f..a67c2749089a 100644
--- a/Documentation/userspace-api/media/v4l/dev-subdev.rst
+++ b/Documentation/userspace-api/media/v4l/dev-subdev.rst
@@ -29,6 +29,8 @@ will feature a character device node on which ioctls can be called to
- negotiate image formats on individual pads
+- inspect and modify internal data routing between pads of the same entity
+
Sub-device character device nodes, conventionally named
``/dev/v4l-subdev*``, use major number 81.
diff --git a/Documentation/userspace-api/media/v4l/user-func.rst b/Documentation/userspace-api/media/v4l/user-func.rst
index 53e604bd7d60..228c1521f190 100644
--- a/Documentation/userspace-api/media/v4l/user-func.rst
+++ b/Documentation/userspace-api/media/v4l/user-func.rst
@@ -70,6 +70,7 @@ Function Reference
vidioc-subdev-g-crop
vidioc-subdev-g-fmt
vidioc-subdev-g-frame-interval
+ vidioc-subdev-g-routing
vidioc-subdev-g-selection
vidioc-subdev-querycap
vidioc-subscribe-event
diff --git a/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst b/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst
new file mode 100644
index 000000000000..a0d9c79e162f
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst
@@ -0,0 +1,150 @@
+.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+.. c:namespace:: V4L
+
+.. _VIDIOC_SUBDEV_G_ROUTING:
+
+******************************************************
+ioctl VIDIOC_SUBDEV_G_ROUTING, VIDIOC_SUBDEV_S_ROUTING
+******************************************************
+
+Name
+====
+
+VIDIOC_SUBDEV_G_ROUTING - VIDIOC_SUBDEV_S_ROUTING - Get or set routing between streams of media pads in a media entity.
+
+
+Synopsis
+========
+
+.. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_G_ROUTING, struct v4l2_subdev_routing *argp )
+ :name: VIDIOC_SUBDEV_G_ROUTING
+
+.. c:function:: int ioctl( int fd, VIDIOC_SUBDEV_S_ROUTING, struct v4l2_subdev_routing *argp )
+ :name: VIDIOC_SUBDEV_S_ROUTING
+
+
+Arguments
+=========
+
+``fd``
+ File descriptor returned by :ref:`open() <func-open>`.
+
+``argp``
+ Pointer to struct :c:type:`v4l2_subdev_routing`.
+
+
+Description
+===========
+
+These ioctls are used to get and set the routing in a media entity.
+The routing configuration determines the flows of data inside an entity.
+
+Drivers report their current routing tables using the
+``VIDIOC_SUBDEV_G_ROUTING`` ioctl and application may enable or disable routes
+with the ``VIDIOC_SUBDEV_S_ROUTING`` ioctl, by adding or removing routes and
+setting or clearing flags of the ``flags`` field of a
+struct :c:type:`v4l2_subdev_route`.
How about adding:
Routes that have V4L2_SUBDEV_ROUTE_FL_IMMUTABLE flag cannot be removed.
Depending on the driver, their V4L2_SUBDEV_ROUTE_FL_ACTIVE flag may be set
or reset.
I have dropped the IMMUTABLE flag in my WIP branch, as I couldn't figure
out a use for it. The only immutable routes are source routes, which are
already special and there's no need for an extra flag.
Also see a comment later on.
+
+All stream configurations are reset when ``VIDIOC_SUBDEV_S_ROUTING`` is called. This
+means that the userspace mut reconfigure all streams after calling the ioctl
+with e.g. ``VIDIOC_SUBDEV_S_FMT``.
How about this:
Calling ``VIDIOC_SUBDEV_S_ROUTING`` will cause the selections and subdev
formats being propagated from the sink pads towards the sources.
Hmm, but that's not true. The selections and formats will be zeroed,
unless the driver initializes them to a value. There's no propagation done.
+
+A special case for routing are routes marked with
+``V4L2_SUBDEV_ROUTE_FL_SOURCE`` flag. These routes are used to describe
+source endpoints on sensors and the sink fields are unused.
+
+When inspecting routes through ``VIDIOC_SUBDEV_G_ROUTING`` and the application
+provided ``num_routes`` is not big enough to contain all the available routes
+the subdevice exposes, drivers return the ENOSPC error code and adjust the
+value of the ``num_routes`` field. Application should then reserve enough memory
+for all the route entries and call ``VIDIOC_SUBDEV_G_ROUTING`` again.
+
+.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
+
+.. c:type:: v4l2_subdev_routing
+
+.. flat-table:: struct v4l2_subdev_routing
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 1 2
+
+ * - __u32
+ - ``which``
+ - Format to modified, from enum
+ :ref:`v4l2_subdev_format_whence <v4l2-subdev-format-whence>`.
+ * - struct :c:type:`v4l2_subdev_route`
+ - ``routes[]``
+ - Array of struct :c:type:`v4l2_subdev_route` entries
+ * - __u32
+ - ``num_routes``
+ - Number of entries of the routes array
+ * - __u32
+ - ``reserved``\ [5]
+ - Reserved for future extensions. Applications and drivers must set
+ the array to zero.
+
+.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
+
+.. c:type:: v4l2_subdev_route
+
+.. flat-table:: struct v4l2_subdev_route
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 1 1 2
+
+ * - __u32
+ - ``sink_pad``
+ - Sink pad number.
+ * - __u32
+ - ``sink_stream``
+ - Sink pad stream number.
+ * - __u32
+ - ``source_pad``
+ - Source pad number.
+ * - __u32
+ - ``source_stream``
+ - Source pad stream number.
+ * - __u32
+ - ``flags``
+ - Route enable/disable flags
+ :ref:`v4l2_subdev_routing_flags <v4l2-subdev-routing-flags>`.
+ * - __u32
+ - ``reserved``\ [5]
+ - Reserved for future extensions. Applications and drivers must set
+ the array to zero.
+
+.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
+
+.. _v4l2-subdev-routing-flags:
+
+.. flat-table:: enum v4l2_subdev_routing_flags
+ :header-rows: 0
+ :stub-columns: 0
+ :widths: 3 1 4
+
+ * - V4L2_SUBDEV_ROUTE_FL_ACTIVE
+ - 0
+ - The route is enabled. Set by applications.
+ * - V4L2_SUBDEV_ROUTE_FL_IMMUTABLE
How about calling this STATIC instead of IMMUTABLE? IMMUTABLE is used as a
link flag to mean a link that may not be changed in any way. In this case
we rather want to say that the route is always there, albeit you can still
enable or disable it.
If we think there's a need for this, I can add it back and name it
static. I think what it then should mean is that the user can
enable/disable it and also set the stream id, but the route must always
exist.
But as I said above, I haven't figured out a use for this.
+ - 1
+ - The route is immutable. Set by the driver.
+ * - V4L2_SUBDEV_ROUTE_FL_SOURCE
+ - 2
+ - The route is a source route, and the ``sink_pad`` and ``sink_stream``
+ fields are unused. Set by the driver.
+
+Return Value
+============
+
+On success 0 is returned, on error -1 and the ``errno`` variable is set
+appropriately. The generic error codes are described at the
+:ref:`Generic Error Codes <gen-errors>` chapter.
+
+ENOSPC
+ The number of provided route entries is less than the available ones.
What does "available ones" mean in this context? More than is supported?
Wouldn't E2BIG be the appropriate code in that case?
Good question. I don't think I wrote this part =). ENOSPC refers to the
case where VIDIOC_SUBDEV_G_ROUTING is called without enough space for
the routing table. So "available ones" mean the routes in the subdev's
routing table, and "provided route entries" refers to the userspace
target routing table.
It sounds pretty odd, and obviously needs a clarification.
Tomi
