diff options
Diffstat (limited to 'Documentation/userspace-api/media')
| -rw-r--r-- | Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst | 46 |
1 files changed, 32 insertions, 14 deletions
diff --git a/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst b/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst index 26b5004bfe6d..cbd9370006b6 100644 --- a/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst +++ b/Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst @@ -43,23 +43,38 @@ 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`. +setting or clearing flags of the ``flags`` field of a struct +:c:type:`v4l2_subdev_route`. -All stream configurations are reset when ``VIDIOC_SUBDEV_S_ROUTING`` is called. This -means that the userspace must reconfigure all streams after calling the ioctl -with e.g. ``VIDIOC_SUBDEV_S_FMT``. +All stream configurations are reset when ``VIDIOC_SUBDEV_S_ROUTING`` is called. +This means that the userspace must reconfigure all stream formats and selections +after calling the ioctl with e.g. ``VIDIOC_SUBDEV_S_FMT``. Only subdevices which have both sink and source pads can support routing. -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. - -On a successful ``VIDIOC_SUBDEV_G_ROUTING`` call the driver updates the -``num_routes`` field to reflect the actual number of routes returned. +The ``len_routes`` field indicates the number of routes that can fit in the +``routes`` array allocated by userspace. It is set by applications for both +ioctls to indicate how many routes the kernel can return, and is never modified +by the kernel. + +The ``num_routes`` field indicates the number of routes in the routing +table. For ``VIDIOC_SUBDEV_S_ROUTING``, it is set by userspace to the number of +routes that the application stored in the ``routes`` array. For both ioctls, it +is returned by the kernel and indicates how many routes are stored in the +subdevice routing table. This may be smaller or larger than the value of +``num_routes`` set by the application for ``VIDIOC_SUBDEV_S_ROUTING``, as +drivers may adjust the requested routing table. + +The kernel can return a ``num_routes`` value larger than ``len_routes`` from +both ioctls. This indicates thare are more routes in the routing table than fits +the ``routes`` array. In this case, the ``routes`` array is filled by the kernel +with the first ``len_routes`` entries of the subdevice routing table. This is +not considered to be an error, and the ioctl call succeeds. If the applications +wants to retrieve the missing routes, it can issue a new +``VIDIOC_SUBDEV_G_ROUTING`` call with a large enough ``routes`` array. + +``VIDIOC_SUBDEV_S_ROUTING`` may return more routes than the user provided in +``num_routes`` field due to e.g. hardware properties. .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| @@ -74,6 +89,9 @@ On a successful ``VIDIOC_SUBDEV_G_ROUTING`` call the driver updates the - ``which`` - Routing table to be accessed, from enum :ref:`v4l2_subdev_format_whence <v4l2-subdev-format-whence>`. + * - __u32 + - ``len_routes`` + - The length of the array (as in memory reserved for the array) * - struct :c:type:`v4l2_subdev_route` - ``routes[]`` - Array of struct :c:type:`v4l2_subdev_route` entries @@ -81,7 +99,7 @@ On a successful ``VIDIOC_SUBDEV_G_ROUTING`` call the driver updates the - ``num_routes`` - Number of entries of the routes array * - __u32 - - ``reserved``\ [5] + - ``reserved``\ [11] - Reserved for future extensions. Applications and drivers must set the array to zero. |