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diff --git a/Documentation/userspace-api/media/v4l/vidioc-dbg-g-register.rst b/Documentation/userspace-api/media/v4l/vidioc-dbg-g-register.rst new file mode 100644 index 000000000000..6311a63278a5 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/vidioc-dbg-g-register.rst @@ -0,0 +1,171 @@ +.. Permission is granted to copy, distribute and/or modify this +.. document under the terms of the GNU Free Documentation License, +.. Version 1.1 or any later version published by the Free Software +.. Foundation, with no Invariant Sections, no Front-Cover Texts +.. and no Back-Cover Texts. A copy of the license is included at +.. Documentation/userspace-api/media/fdl-appendix.rst. +.. +.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections + +.. _VIDIOC_DBG_G_REGISTER: + +************************************************** +ioctl VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER +************************************************** + +Name +==== + +VIDIOC_DBG_G_REGISTER - VIDIOC_DBG_S_REGISTER - Read or write hardware registers + + +Synopsis +======== + +.. c:function:: int ioctl( int fd, VIDIOC_DBG_G_REGISTER, struct v4l2_dbg_register *argp ) + :name: VIDIOC_DBG_G_REGISTER + +.. c:function:: int ioctl( int fd, VIDIOC_DBG_S_REGISTER, const struct v4l2_dbg_register *argp ) + :name: VIDIOC_DBG_S_REGISTER + + +Arguments +========= + +``fd`` + File descriptor returned by :ref:`open() <func-open>`. + +``argp`` + Pointer to struct :c:type:`v4l2_dbg_register`. + + +Description +=========== + +.. note:: + + This is an :ref:`experimental` interface and may + change in the future. + +For driver debugging purposes these ioctls allow test applications to +access hardware registers directly. Regular applications must not use +them. + +Since writing or even reading registers can jeopardize the system +security, its stability and damage the hardware, both ioctls require +superuser privileges. Additionally the Linux kernel must be compiled +with the ``CONFIG_VIDEO_ADV_DEBUG`` option to enable these ioctls. + +To write a register applications must initialize all fields of a struct +:c:type:`v4l2_dbg_register` except for ``size`` and +call ``VIDIOC_DBG_S_REGISTER`` with a pointer to this structure. The +``match.type`` and ``match.addr`` or ``match.name`` fields select a chip +on the TV card, the ``reg`` field specifies a register number and the +``val`` field the value to be written into the register. + +To read a register applications must initialize the ``match.type``, +``match.addr`` or ``match.name`` and ``reg`` fields, and call +``VIDIOC_DBG_G_REGISTER`` with a pointer to this structure. On success +the driver stores the register value in the ``val`` field and the size +(in bytes) of the value in ``size``. + +When ``match.type`` is ``V4L2_CHIP_MATCH_BRIDGE``, ``match.addr`` +selects the nth non-sub-device chip on the TV card. The number zero +always selects the host chip, e. g. the chip connected to the PCI or USB +bus. You can find out which chips are present with the +:ref:`VIDIOC_DBG_G_CHIP_INFO` ioctl. + +When ``match.type`` is ``V4L2_CHIP_MATCH_SUBDEV``, ``match.addr`` +selects the nth sub-device. + +These ioctls are optional, not all drivers may support them. However +when a driver supports these ioctls it must also support +:ref:`VIDIOC_DBG_G_CHIP_INFO`. Conversely +it may support ``VIDIOC_DBG_G_CHIP_INFO`` but not these ioctls. + +``VIDIOC_DBG_G_REGISTER`` and ``VIDIOC_DBG_S_REGISTER`` were introduced +in Linux 2.6.21, but their API was changed to the one described here in +kernel 2.6.29. + +We recommended the v4l2-dbg utility over calling these ioctls directly. +It is available from the LinuxTV v4l-dvb repository; see +`https://linuxtv.org/repo/ <https://linuxtv.org/repo/>`__ for access +instructions. + + +.. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{7.0cm}| + +.. c:type:: v4l2_dbg_match + +.. flat-table:: struct v4l2_dbg_match + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 2 + + * - __u32 + - ``type`` + - See :ref:`chip-match-types` for a list of possible types. + * - union { + - (anonymous) + * - __u32 + - ``addr`` + - Match a chip by this number, interpreted according to the ``type`` + field. + * - char + - ``name[32]`` + - Match a chip by this name, interpreted according to the ``type`` + field. Currently unused. + * - } + - + + + +.. c:type:: v4l2_dbg_register + +.. flat-table:: struct v4l2_dbg_register + :header-rows: 0 + :stub-columns: 0 + + * - struct v4l2_dbg_match + - ``match`` + - How to match the chip, see :c:type:`v4l2_dbg_match`. + * - __u32 + - ``size`` + - The register size in bytes. + * - __u64 + - ``reg`` + - A register number. + * - __u64 + - ``val`` + - The value read from, or to be written into the register. + + + +.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| + +.. _chip-match-types: + +.. flat-table:: Chip Match Types + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 4 + + * - ``V4L2_CHIP_MATCH_BRIDGE`` + - 0 + - Match the nth chip on the card, zero for the bridge chip. Does not + match sub-devices. + * - ``V4L2_CHIP_MATCH_SUBDEV`` + - 4 + - Match the nth sub-device. + + +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. + +EPERM + Insufficient permissions. Root privileges are required to execute + these ioctls. |