mirror of https://gitee.com/openkylin/linux.git
[media] doc-rst: add documentation for uvcvideo
Convert it to ReST and add to media/v4l-drivers book. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
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@ -39,4 +39,5 @@ License".
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si4713
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si476x
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soc-camera
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uvcvideo
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zr364xx
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@ -1,5 +1,5 @@
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Linux USB Video Class (UVC) driver
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==================================
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The Linux USB Video Class (UVC) driver
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======================================
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This file documents some driver-specific aspects of the UVC driver, such as
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driver-specific ioctls and implementation notes.
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@ -11,7 +11,8 @@ linux-uvc-devel@lists.berlios.de.
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Extension Unit (XU) support
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---------------------------
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1. Introduction
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Introduction
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~~~~~~~~~~~~
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The UVC specification allows for vendor-specific extensions through extension
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units (XUs). The Linux UVC driver supports extension unit controls (XU controls)
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@ -31,7 +32,8 @@ maximum flexibility.
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Both mechanisms complement each other and are described in more detail below.
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2. Control mappings
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Control mappings
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~~~~~~~~~~~~~~~~
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The UVC driver provides an API for user space applications to define so-called
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control mappings at runtime. These allow for individual XU controls or byte
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@ -82,7 +84,8 @@ For details on the UVCIOC_CTRL_QUERY ioctl please refer to the section titled
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"IOCTL reference" below.
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4. Security
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Security
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~~~~~~~~
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The API doesn't currently provide a fine-grained access control facility. The
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UVCIOC_CTRL_ADD and UVCIOC_CTRL_MAP ioctls require super user permissions.
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@ -90,20 +93,24 @@ UVCIOC_CTRL_ADD and UVCIOC_CTRL_MAP ioctls require super user permissions.
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Suggestions on how to improve this are welcome.
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5. Debugging
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Debugging
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~~~~~~~~~
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In order to debug problems related to XU controls or controls in general it is
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recommended to enable the UVC_TRACE_CONTROL bit in the module parameter 'trace'.
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This causes extra output to be written into the system log.
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6. IOCTL reference
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IOCTL reference
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~~~~~~~~~~~~~~~
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---- UVCIOC_CTRL_MAP - Map a UVC control to a V4L2 control ----
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UVCIOC_CTRL_MAP - Map a UVC control to a V4L2 control
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Argument: struct uvc_xu_control_mapping
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Description:
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**Description**:
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This ioctl creates a mapping between a UVC control or part of a UVC
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control and a V4L2 control. Once mappings are defined, userspace
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applications can access vendor-defined UVC control through the V4L2
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@ -122,7 +129,8 @@ Description:
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For signed integer V4L2 controls the data_type field should be set to
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UVC_CTRL_DATA_TYPE_SIGNED. Other values are currently ignored.
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Return value:
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**Return value**:
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On success 0 is returned. On error -1 is returned and errno is set
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appropriately.
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EEXIST
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Mapping already exists.
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Data types:
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**Data types**:
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.. code-block:: none
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* struct uvc_xu_control_mapping
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__u32 id V4L2 control identifier
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UVC_CTRL_DATA_TYPE_BITMASK Bitmask
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---- UVCIOC_CTRL_QUERY - Query a UVC XU control ----
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UVCIOC_CTRL_QUERY - Query a UVC XU control
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Argument: struct uvc_xu_control_query
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Description:
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**Description**:
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This ioctl queries a UVC XU control identified by its extension unit ID
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and control selector.
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@ -213,7 +225,8 @@ Description:
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important for the result of the UVC_GET_LEN requests, which is always
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returned as a little-endian 16-bit integer by the device.
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Return value:
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**Return value**:
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On success 0 is returned. On error -1 is returned and errno is set
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appropriately.
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EFAULT
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The data pointer references an inaccessible memory area.
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Data types:
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**Data types**:
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.. code-block:: none
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* struct uvc_xu_control_query
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__u8 unit Extension unit ID
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