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218 lines
9.3 KiB
Diff
218 lines
9.3 KiB
Diff
From c1a630e792140b4791bad84974e31b4a1cf09b1b Mon Sep 17 00:00:00 2001
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From: Jacopo Mondi <jacopo@jmondi.org>
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Date: Tue, 7 Apr 2020 17:21:56 +0200
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Subject: [PATCH] Documentation: media: Document read-only subdevice
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Document a new kAPI function to register subdev device nodes in read only
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mode and for each affected ioctl report how access is restricted.
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Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
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Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
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---
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Documentation/media/kapi/v4l2-subdev.rst | 44 +++++++++++++++++++
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Documentation/media/uapi/v4l/dev-subdev.rst | 5 +++
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.../media/uapi/v4l/vidioc-g-dv-timings.rst | 6 +++
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Documentation/media/uapi/v4l/vidioc-g-std.rst | 6 +++
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.../media/uapi/v4l/vidioc-subdev-g-crop.rst | 9 ++++
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.../media/uapi/v4l/vidioc-subdev-g-fmt.rst | 8 ++++
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.../v4l/vidioc-subdev-g-frame-interval.rst | 8 ++++
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.../uapi/v4l/vidioc-subdev-g-selection.rst | 8 ++++
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8 files changed, 94 insertions(+)
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--- a/Documentation/media/kapi/v4l2-subdev.rst
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+++ b/Documentation/media/kapi/v4l2-subdev.rst
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@@ -332,6 +332,50 @@ Private ioctls
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All ioctls not in the above list are passed directly to the sub-device
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driver through the core::ioctl operation.
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+Read-only sub-device userspace API
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+----------------------------------
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+
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+Bridge drivers that control their connected subdevices through direct calls to
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+the kernel API realized by :c:type:`v4l2_subdev_ops` structure do not usually
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+want userspace to be able to change the same parameters through the subdevice
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+device node and thus do not usually register any.
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+
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+It is sometimes useful to report to userspace the current subdevice
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+configuration through a read-only API, that does not permit applications to
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+change to the device parameters but allows interfacing to the subdevice device
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+node to inspect them.
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+
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+For instance, to implement cameras based on computational photography, userspace
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+needs to know the detailed camera sensor configuration (in terms of skipping,
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+binning, cropping and scaling) for each supported output resolution. To support
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+such use cases, bridge drivers may expose the subdevice operations to userspace
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+through a read-only API.
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+
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+To create a read-only device node for all the subdevices registered with the
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+``V4L2_SUBDEV_FL_HAS_DEVNODE`` set, the :c:type:`v4l2_device` driver should call
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+:c:func:`v4l2_device_register_ro_subdev_nodes`.
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+
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+Access to the following ioctls for userspace applications is restricted on
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+sub-device device nodes registered with
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+:c:func:`v4l2_device_register_ro_subdev_nodes`.
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+
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+``VIDIOC_SUBDEV_S_FMT``,
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+``VIDIOC_SUBDEV_S_CROP``,
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+``VIDIOC_SUBDEV_S_SELECTION``:
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+
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+ These ioctls are only allowed on a read-only subdevice device node
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+ for the :ref:`V4L2_SUBDEV_FORMAT_TRY <v4l2-subdev-format-whence>`
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+ formats and selection rectangles.
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+
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+``VIDIOC_SUBDEV_S_FRAME_INTERVAL``,
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+``VIDIOC_SUBDEV_S_DV_TIMINGS``,
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+``VIDIOC_SUBDEV_S_STD``:
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+
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+ These ioctls are not allowed on a read-only subdevice node.
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+
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+In case the ioctl is not allowed, or the format to modify is set to
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+``V4L2_SUBDEV_FORMAT_ACTIVE``, the core returns a negative error code and
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+the errno variable is set to ``-EPERM``.
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I2C sub-device drivers
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----------------------
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--- a/Documentation/media/uapi/v4l/dev-subdev.rst
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+++ b/Documentation/media/uapi/v4l/dev-subdev.rst
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@@ -39,6 +39,11 @@ will feature a character device node on
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Sub-device character device nodes, conventionally named
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``/dev/v4l-subdev*``, use major number 81.
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+Drivers may opt to limit the sub-device character devices to only expose
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+operations that do not modify the device state. In such a case the sub-devices
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+are referred to as ``read-only`` in the rest of this documentation, and the
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+related restrictions are documented in individual ioctls.
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+
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Controls
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========
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--- a/Documentation/media/uapi/v4l/vidioc-g-dv-timings.rst
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+++ b/Documentation/media/uapi/v4l/vidioc-g-dv-timings.rst
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@@ -57,6 +57,10 @@ pointer to the struct :c:type:`v4l2_dv_t
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structure as argument. If the ioctl is not supported or the timing
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values are not correct, the driver returns ``EINVAL`` error code.
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+Calling ``VIDIOC_SUBDEV_S_DV_TIMINGS`` on a subdev device node that has been
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+registered in read-only mode is not allowed. An error is returned and the errno
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+variable is set to ``-EPERM``.
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+
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The ``linux/v4l2-dv-timings.h`` header can be used to get the timings of
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the formats in the :ref:`cea861` and :ref:`vesadmt` standards. If
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the current input or output does not support DV timings (e.g. if
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@@ -81,6 +85,8 @@ ENODATA
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EBUSY
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The device is busy and therefore can not change the timings.
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+EPERM
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+ ``VIDIOC_SUBDEV_S_DV_TIMINGS`` has been called on a read-only subdevice.
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
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--- a/Documentation/media/uapi/v4l/vidioc-g-std.rst
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+++ b/Documentation/media/uapi/v4l/vidioc-g-std.rst
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@@ -66,6 +66,9 @@ video timings (e.g. if :ref:`VIDIOC_ENUM
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does not set the ``V4L2_IN_CAP_STD`` flag), then ``ENODATA`` error code is
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returned.
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+Calling ``VIDIOC_SUBDEV_S_STD`` on a subdev device node that has been registered
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+in read-only mode is not allowed. An error is returned and the errno variable is
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+set to ``-EPERM``.
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Return Value
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============
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@@ -79,3 +82,6 @@ EINVAL
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ENODATA
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Standard video timings are not supported for this input or output.
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+
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+EPERM
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+ ``VIDIOC_SUBDEV_S_STD`` has been called on a read-only subdevice.
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--- a/Documentation/media/uapi/v4l/vidioc-subdev-g-crop.rst
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+++ b/Documentation/media/uapi/v4l/vidioc-subdev-g-crop.rst
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@@ -73,6 +73,11 @@ crop rectangles and stored in the sub-de
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applications querying the same sub-device would thus not interact with
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each other.
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+If the subdev device node has been registered in read-only mode, calls to
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+``VIDIOC_SUBDEV_S_CROP`` are only valid if the ``which`` field is set to
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+``V4L2_SUBDEV_FORMAT_TRY``, otherwise an error is returned and the errno
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+variable is set to ``-EPERM``.
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+
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Drivers must not return an error solely because the requested crop
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rectangle doesn't match the device capabilities. They must instead
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modify the rectangle to match what the hardware can provide. The
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@@ -123,3 +128,7 @@ EINVAL
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references a non-existing pad, the ``which`` field references a
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non-existing format, or cropping is not supported on the given
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subdev pad.
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+
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+EPERM
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+ The ``VIDIOC_SUBDEV_S_CROP`` ioctl has been called on a read-only subdevice
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+ and the ``which`` field is set to ``V4L2_SUBDEV_FORMAT_ACTIVE``.
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--- a/Documentation/media/uapi/v4l/vidioc-subdev-g-fmt.rst
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+++ b/Documentation/media/uapi/v4l/vidioc-subdev-g-fmt.rst
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@@ -78,6 +78,11 @@ current links configuration or sub-devic
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a low-pass noise filter might crop pixels at the frame boundaries,
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modifying its output frame size.
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+If the subdev device node has been registered in read-only mode, calls to
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+``VIDIOC_SUBDEV_S_FMT`` are only valid if the ``which`` field is set to
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+``V4L2_SUBDEV_FORMAT_TRY``, otherwise an error is returned and the errno
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+variable is set to ``-EPERM``.
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+
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Drivers must not return an error solely because the requested format
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doesn't match the device capabilities. They must instead modify the
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format to match what the hardware can provide. The modified format
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@@ -146,6 +151,9 @@ EINVAL
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``pad`` references a non-existing pad, or the ``which`` field
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references a non-existing format.
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+EPERM
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+ The ``VIDIOC_SUBDEV_S_FMT`` ioctl has been called on a read-only subdevice
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+ and the ``which`` field is set to ``V4L2_SUBDEV_FORMAT_ACTIVE``.
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============
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--- a/Documentation/media/uapi/v4l/vidioc-subdev-g-frame-interval.rst
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+++ b/Documentation/media/uapi/v4l/vidioc-subdev-g-frame-interval.rst
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@@ -65,6 +65,10 @@ struct
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contains the current frame interval as would be returned by a
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``VIDIOC_SUBDEV_G_FRAME_INTERVAL`` call.
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+Calling ``VIDIOC_SUBDEV_S_FRAME_INTERVAL`` on a subdev device node that has been
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+registered in read-only mode is not allowed. An error is returned and the errno
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+variable is set to ``-EPERM``.
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+
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Drivers must not return an error solely because the requested interval
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doesn't match the device capabilities. They must instead modify the
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interval to match what the hardware can provide. The modified interval
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@@ -118,3 +122,7 @@ EINVAL
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:c:type:`v4l2_subdev_frame_interval`
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``pad`` references a non-existing pad, or the pad doesn't support
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frame intervals.
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+
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+EPERM
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+ The ``VIDIOC_SUBDEV_S_FRAME_INTERVAL`` ioctl has been called on a read-only
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+ subdevice.
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--- a/Documentation/media/uapi/v4l/vidioc-subdev-g-selection.rst
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+++ b/Documentation/media/uapi/v4l/vidioc-subdev-g-selection.rst
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@@ -53,6 +53,10 @@ function of the crop API, and more, are
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See :ref:`subdev` for more information on how each selection target
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affects the image processing pipeline inside the subdevice.
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+If the subdev device node has been registered in read-only mode, calls to
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+``VIDIOC_SUBDEV_S_SELECTION`` are only valid if the ``which`` field is set to
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+``V4L2_SUBDEV_FORMAT_TRY``, otherwise an error is returned and the errno
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+variable is set to ``-EPERM``.
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Types of selection targets
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--------------------------
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@@ -123,3 +127,7 @@ EINVAL
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``pad`` references a non-existing pad, the ``which`` field
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references a non-existing format, or the selection target is not
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supported on the given subdev pad.
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+
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+EPERM
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+ The ``VIDIOC_SUBDEV_S_SELECTION`` ioctl has been called on a read-only
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+ subdevice and the ``which`` field is set to ``V4L2_SUBDEV_FORMAT_ACTIVE``.
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