[media] v4l2-subdev.rst: add two sections from v4l2-framework.rst
There are two additional subdev-specific sections at the v4l2-framework file. Move them to the subdev chapter, in order to better organize the book. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
This commit is contained in:
Mauro Carvalho Chehab
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2873f4db2a
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@ -80,171 +80,6 @@ The V4L2 framework also optionally integrates with the media framework. If a
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driver sets the struct v4l2_device mdev field, sub-devices and video nodes
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will automatically appear in the media framework as entities.
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V4L2 sub-device userspace API
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-----------------------------
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Beside exposing a kernel API through the v4l2_subdev_ops structure, V4L2
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sub-devices can also be controlled directly by userspace applications.
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Device nodes named v4l-subdevX can be created in /dev to access sub-devices
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directly. If a sub-device supports direct userspace configuration it must set
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the V4L2_SUBDEV_FL_HAS_DEVNODE flag before being registered.
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After registering sub-devices, the v4l2_device driver can create device nodes
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for all registered sub-devices marked with V4L2_SUBDEV_FL_HAS_DEVNODE by calling
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v4l2_device_register_subdev_nodes(). Those device nodes will be automatically
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removed when sub-devices are unregistered.
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The device node handles a subset of the V4L2 API.
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VIDIOC_QUERYCTRL
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VIDIOC_QUERYMENU
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VIDIOC_G_CTRL
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VIDIOC_S_CTRL
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VIDIOC_G_EXT_CTRLS
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VIDIOC_S_EXT_CTRLS
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VIDIOC_TRY_EXT_CTRLS
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The controls ioctls are identical to the ones defined in V4L2. They
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behave identically, with the only exception that they deal only with
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controls implemented in the sub-device. Depending on the driver, those
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controls can be also be accessed through one (or several) V4L2 device
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nodes.
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VIDIOC_DQEVENT
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VIDIOC_SUBSCRIBE_EVENT
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VIDIOC_UNSUBSCRIBE_EVENT
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The events ioctls are identical to the ones defined in V4L2. They
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behave identically, with the only exception that they deal only with
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events generated by the sub-device. Depending on the driver, those
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events can also be reported by one (or several) V4L2 device nodes.
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Sub-device drivers that want to use events need to set the
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V4L2_SUBDEV_USES_EVENTS v4l2_subdev::flags and initialize
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v4l2_subdev::nevents to events queue depth before registering the
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sub-device. After registration events can be queued as usual on the
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v4l2_subdev::devnode device node.
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To properly support events, the poll() file operation is also
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implemented.
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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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I2C sub-device drivers
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----------------------
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Since these drivers are so common, special helper functions are available to
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ease the use of these drivers (v4l2-common.h).
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The recommended method of adding v4l2_subdev support to an I2C driver is to
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embed the v4l2_subdev struct into the state struct that is created for each
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I2C device instance. Very simple devices have no state struct and in that case
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you can just create a v4l2_subdev directly.
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A typical state struct would look like this (where 'chipname' is replaced by
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the name of the chip):
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.. code-block:: none
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struct chipname_state {
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struct v4l2_subdev sd;
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... /* additional state fields */
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};
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Initialize the v4l2_subdev struct as follows:
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.. code-block:: none
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v4l2_i2c_subdev_init(&state->sd, client, subdev_ops);
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This function will fill in all the fields of v4l2_subdev and ensure that the
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v4l2_subdev and i2c_client both point to one another.
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You should also add a helper inline function to go from a v4l2_subdev pointer
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to a chipname_state struct:
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.. code-block:: none
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static inline struct chipname_state *to_state(struct v4l2_subdev *sd)
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{
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return container_of(sd, struct chipname_state, sd);
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}
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Use this to go from the v4l2_subdev struct to the i2c_client struct:
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.. code-block:: none
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struct i2c_client *client = v4l2_get_subdevdata(sd);
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And this to go from an i2c_client to a v4l2_subdev struct:
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.. code-block:: none
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struct v4l2_subdev *sd = i2c_get_clientdata(client);
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Make sure to call v4l2_device_unregister_subdev(sd) when the remove() callback
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is called. This will unregister the sub-device from the bridge driver. It is
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safe to call this even if the sub-device was never registered.
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You need to do this because when the bridge driver destroys the i2c adapter
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the remove() callbacks are called of the i2c devices on that adapter.
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After that the corresponding v4l2_subdev structures are invalid, so they
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have to be unregistered first. Calling v4l2_device_unregister_subdev(sd)
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from the remove() callback ensures that this is always done correctly.
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The bridge driver also has some helper functions it can use:
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.. code-block:: none
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struct v4l2_subdev *sd = v4l2_i2c_new_subdev(v4l2_dev, adapter,
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"module_foo", "chipid", 0x36, NULL);
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This loads the given module (can be NULL if no module needs to be loaded) and
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calls i2c_new_device() with the given i2c_adapter and chip/address arguments.
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If all goes well, then it registers the subdev with the v4l2_device.
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You can also use the last argument of v4l2_i2c_new_subdev() to pass an array
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of possible I2C addresses that it should probe. These probe addresses are
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only used if the previous argument is 0. A non-zero argument means that you
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know the exact i2c address so in that case no probing will take place.
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Both functions return NULL if something went wrong.
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Note that the chipid you pass to v4l2_i2c_new_subdev() is usually
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the same as the module name. It allows you to specify a chip variant, e.g.
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"saa7114" or "saa7115". In general though the i2c driver autodetects this.
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The use of chipid is something that needs to be looked at more closely at a
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later date. It differs between i2c drivers and as such can be confusing.
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To see which chip variants are supported you can look in the i2c driver code
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for the i2c_device_id table. This lists all the possibilities.
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There are two more helper functions:
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v4l2_i2c_new_subdev_cfg: this function adds new irq and platform_data
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arguments and has both 'addr' and 'probed_addrs' arguments: if addr is not
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0 then that will be used (non-probing variant), otherwise the probed_addrs
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are probed.
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For example: this will probe for address 0x10:
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.. code-block:: none
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struct v4l2_subdev *sd = v4l2_i2c_new_subdev_cfg(v4l2_dev, adapter,
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"module_foo", "chipid", 0, NULL, 0, I2C_ADDRS(0x10));
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v4l2_i2c_new_subdev_board uses an i2c_board_info struct which is passed
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to the i2c driver and replaces the irq, platform_data and addr arguments.
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If the subdev supports the s_config core ops, then that op is called with
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the irq and platform_data arguments after the subdev was setup. The older
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v4l2_i2c_new_(probed\_)subdev functions will call s_config as well, but with
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irq set to 0 and platform_data set to NULL.
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struct video_device
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-------------------
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@ -262,6 +262,172 @@ is called. After all subdevices have been located the .complete() callback is
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called. When a subdevice is removed from the system the .unbind() method is
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called. All three callbacks are optional.
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V4L2 sub-device userspace API
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-----------------------------
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Beside exposing a kernel API through the v4l2_subdev_ops structure, V4L2
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sub-devices can also be controlled directly by userspace applications.
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Device nodes named v4l-subdevX can be created in /dev to access sub-devices
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directly. If a sub-device supports direct userspace configuration it must set
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the V4L2_SUBDEV_FL_HAS_DEVNODE flag before being registered.
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After registering sub-devices, the v4l2_device driver can create device nodes
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for all registered sub-devices marked with V4L2_SUBDEV_FL_HAS_DEVNODE by calling
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v4l2_device_register_subdev_nodes(). Those device nodes will be automatically
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removed when sub-devices are unregistered.
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The device node handles a subset of the V4L2 API.
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VIDIOC_QUERYCTRL
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VIDIOC_QUERYMENU
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VIDIOC_G_CTRL
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VIDIOC_S_CTRL
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VIDIOC_G_EXT_CTRLS
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VIDIOC_S_EXT_CTRLS
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VIDIOC_TRY_EXT_CTRLS
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The controls ioctls are identical to the ones defined in V4L2. They
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behave identically, with the only exception that they deal only with
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controls implemented in the sub-device. Depending on the driver, those
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controls can be also be accessed through one (or several) V4L2 device
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nodes.
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VIDIOC_DQEVENT
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VIDIOC_SUBSCRIBE_EVENT
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VIDIOC_UNSUBSCRIBE_EVENT
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The events ioctls are identical to the ones defined in V4L2. They
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behave identically, with the only exception that they deal only with
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events generated by the sub-device. Depending on the driver, those
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events can also be reported by one (or several) V4L2 device nodes.
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Sub-device drivers that want to use events need to set the
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V4L2_SUBDEV_USES_EVENTS v4l2_subdev::flags and initialize
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v4l2_subdev::nevents to events queue depth before registering the
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sub-device. After registration events can be queued as usual on the
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v4l2_subdev::devnode device node.
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To properly support events, the poll() file operation is also
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implemented.
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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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I2C sub-device drivers
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----------------------
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Since these drivers are so common, special helper functions are available to
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ease the use of these drivers (v4l2-common.h).
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The recommended method of adding v4l2_subdev support to an I2C driver is to
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embed the v4l2_subdev struct into the state struct that is created for each
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I2C device instance. Very simple devices have no state struct and in that case
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you can just create a v4l2_subdev directly.
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A typical state struct would look like this (where 'chipname' is replaced by
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the name of the chip):
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.. code-block:: none
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struct chipname_state {
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struct v4l2_subdev sd;
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... /* additional state fields */
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};
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Initialize the v4l2_subdev struct as follows:
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.. code-block:: none
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v4l2_i2c_subdev_init(&state->sd, client, subdev_ops);
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This function will fill in all the fields of v4l2_subdev and ensure that the
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v4l2_subdev and i2c_client both point to one another.
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You should also add a helper inline function to go from a v4l2_subdev pointer
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to a chipname_state struct:
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.. code-block:: none
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static inline struct chipname_state *to_state(struct v4l2_subdev *sd)
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{
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return container_of(sd, struct chipname_state, sd);
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}
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Use this to go from the v4l2_subdev struct to the i2c_client struct:
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.. code-block:: none
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struct i2c_client *client = v4l2_get_subdevdata(sd);
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And this to go from an i2c_client to a v4l2_subdev struct:
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.. code-block:: none
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struct v4l2_subdev *sd = i2c_get_clientdata(client);
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Make sure to call v4l2_device_unregister_subdev(sd) when the remove() callback
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is called. This will unregister the sub-device from the bridge driver. It is
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safe to call this even if the sub-device was never registered.
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You need to do this because when the bridge driver destroys the i2c adapter
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the remove() callbacks are called of the i2c devices on that adapter.
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After that the corresponding v4l2_subdev structures are invalid, so they
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have to be unregistered first. Calling v4l2_device_unregister_subdev(sd)
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from the remove() callback ensures that this is always done correctly.
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The bridge driver also has some helper functions it can use:
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.. code-block:: none
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struct v4l2_subdev *sd = v4l2_i2c_new_subdev(v4l2_dev, adapter,
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"module_foo", "chipid", 0x36, NULL);
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This loads the given module (can be NULL if no module needs to be loaded) and
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calls i2c_new_device() with the given i2c_adapter and chip/address arguments.
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If all goes well, then it registers the subdev with the v4l2_device.
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You can also use the last argument of v4l2_i2c_new_subdev() to pass an array
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of possible I2C addresses that it should probe. These probe addresses are
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only used if the previous argument is 0. A non-zero argument means that you
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know the exact i2c address so in that case no probing will take place.
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Both functions return NULL if something went wrong.
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Note that the chipid you pass to v4l2_i2c_new_subdev() is usually
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the same as the module name. It allows you to specify a chip variant, e.g.
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"saa7114" or "saa7115". In general though the i2c driver autodetects this.
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The use of chipid is something that needs to be looked at more closely at a
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later date. It differs between i2c drivers and as such can be confusing.
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To see which chip variants are supported you can look in the i2c driver code
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for the i2c_device_id table. This lists all the possibilities.
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There are two more helper functions:
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v4l2_i2c_new_subdev_cfg: this function adds new irq and platform_data
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arguments and has both 'addr' and 'probed_addrs' arguments: if addr is not
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0 then that will be used (non-probing variant), otherwise the probed_addrs
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are probed.
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For example: this will probe for address 0x10:
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.. code-block:: none
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struct v4l2_subdev *sd = v4l2_i2c_new_subdev_cfg(v4l2_dev, adapter,
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"module_foo", "chipid", 0, NULL, 0, I2C_ADDRS(0x10));
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v4l2_i2c_new_subdev_board uses an i2c_board_info struct which is passed
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to the i2c driver and replaces the irq, platform_data and addr arguments.
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If the subdev supports the s_config core ops, then that op is called with
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the irq and platform_data arguments after the subdev was setup. The older
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v4l2_i2c_new_(probed\_)subdev functions will call s_config as well, but with
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irq set to 0 and platform_data set to NULL.
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V4L2 subdev kAPI
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^^^^^^^^^^^^^^^^
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