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160 lines
4.6 KiB
160 lines
4.6 KiB
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later |
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.. c:namespace:: V4L |
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.. _VIDIOC_DBG_G_REGISTER: |
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************************************************** |
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ioctl VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER |
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************************************************** |
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Name |
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==== |
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VIDIOC_DBG_G_REGISTER - VIDIOC_DBG_S_REGISTER - Read or write hardware registers |
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Synopsis |
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======== |
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.. c:macro:: VIDIOC_DBG_G_REGISTER |
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``int ioctl(int fd, VIDIOC_DBG_G_REGISTER, struct v4l2_dbg_register *argp)`` |
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.. c:macro:: VIDIOC_DBG_S_REGISTER |
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``int ioctl(int fd, VIDIOC_DBG_S_REGISTER, const struct v4l2_dbg_register *argp)`` |
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Arguments |
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========= |
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``fd`` |
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File descriptor returned by :c:func:`open()`. |
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``argp`` |
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Pointer to struct :c:type:`v4l2_dbg_register`. |
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Description |
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=========== |
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.. note:: |
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This is an :ref:`experimental` interface and may |
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change in the future. |
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For driver debugging purposes these ioctls allow test applications to |
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access hardware registers directly. Regular applications must not use |
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them. |
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Since writing or even reading registers can jeopardize the system |
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security, its stability and damage the hardware, both ioctls require |
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superuser privileges. Additionally the Linux kernel must be compiled |
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with the ``CONFIG_VIDEO_ADV_DEBUG`` option to enable these ioctls. |
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To write a register applications must initialize all fields of a struct |
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:c:type:`v4l2_dbg_register` except for ``size`` and |
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call ``VIDIOC_DBG_S_REGISTER`` with a pointer to this structure. The |
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``match.type`` and ``match.addr`` or ``match.name`` fields select a chip |
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on the TV card, the ``reg`` field specifies a register number and the |
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``val`` field the value to be written into the register. |
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To read a register applications must initialize the ``match.type``, |
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``match.addr`` or ``match.name`` and ``reg`` fields, and call |
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``VIDIOC_DBG_G_REGISTER`` with a pointer to this structure. On success |
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the driver stores the register value in the ``val`` field and the size |
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(in bytes) of the value in ``size``. |
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When ``match.type`` is ``V4L2_CHIP_MATCH_BRIDGE``, ``match.addr`` |
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selects the nth non-sub-device chip on the TV card. The number zero |
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always selects the host chip, e. g. the chip connected to the PCI or USB |
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bus. You can find out which chips are present with the |
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:ref:`VIDIOC_DBG_G_CHIP_INFO` ioctl. |
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When ``match.type`` is ``V4L2_CHIP_MATCH_SUBDEV``, ``match.addr`` |
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selects the nth sub-device. |
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These ioctls are optional, not all drivers may support them. However |
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when a driver supports these ioctls it must also support |
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:ref:`VIDIOC_DBG_G_CHIP_INFO`. Conversely |
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it may support ``VIDIOC_DBG_G_CHIP_INFO`` but not these ioctls. |
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``VIDIOC_DBG_G_REGISTER`` and ``VIDIOC_DBG_S_REGISTER`` were introduced |
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in Linux 2.6.21, but their API was changed to the one described here in |
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kernel 2.6.29. |
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We recommended the v4l2-dbg utility over calling these ioctls directly. |
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It is available from the LinuxTV v4l-dvb repository; see |
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`https://linuxtv.org/repo/ <https://linuxtv.org/repo/>`__ for access |
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instructions. |
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.. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{6.6cm}| |
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.. c:type:: v4l2_dbg_match |
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.. flat-table:: struct v4l2_dbg_match |
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:header-rows: 0 |
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:stub-columns: 0 |
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:widths: 1 1 2 |
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* - __u32 |
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- ``type`` |
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- See :ref:`chip-match-types` for a list of possible types. |
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* - union { |
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- (anonymous) |
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* - __u32 |
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- ``addr`` |
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- Match a chip by this number, interpreted according to the ``type`` |
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field. |
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* - char |
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- ``name[32]`` |
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- Match a chip by this name, interpreted according to the ``type`` |
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field. Currently unused. |
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* - } |
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- |
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.. c:type:: v4l2_dbg_register |
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.. flat-table:: struct v4l2_dbg_register |
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:header-rows: 0 |
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:stub-columns: 0 |
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* - struct v4l2_dbg_match |
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- ``match`` |
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- How to match the chip, see :c:type:`v4l2_dbg_match`. |
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* - __u32 |
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- ``size`` |
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- The register size in bytes. |
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* - __u64 |
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- ``reg`` |
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- A register number. |
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* - __u64 |
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- ``val`` |
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- The value read from, or to be written into the register. |
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.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}| |
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.. _chip-match-types: |
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.. flat-table:: Chip Match Types |
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:header-rows: 0 |
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:stub-columns: 0 |
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:widths: 3 1 4 |
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* - ``V4L2_CHIP_MATCH_BRIDGE`` |
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- 0 |
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- Match the nth chip on the card, zero for the bridge chip. Does not |
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match sub-devices. |
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* - ``V4L2_CHIP_MATCH_SUBDEV`` |
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- 4 |
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- Match the nth sub-device. |
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Return Value |
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============ |
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On success 0 is returned, on error -1 and the ``errno`` variable is set |
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appropriately. The generic error codes are described at the |
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:ref:`Generic Error Codes <gen-errors>` chapter. |
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EPERM |
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Insufficient permissions. Root privileges are required to execute |
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these ioctls.
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