V4L/DVB (9820): v4l2: add v4l2_device and v4l2_subdev structs to the v4l2 framework.

Start implementing a proper v4l2 framework as discussed during the
Linux Plumbers Conference 2008.

Introduces v4l2_device (for device instances) and v4l2_subdev (representing
sub-device instances).
Signed-off-by: NHans Verkuil <hverkuil@xs4all.nl>
Reviewed-by: NLaurent Pinchart <laurent.pinchart@skynet.be>
Reviewed-by: NGuennadi Liakhovetski <g.liakhovetski@gmx.de>
Reviewed-by: NAndy Walls <awalls@radix.net>
Reviewed-by: NDavid Brownell <david-b@pacbell.net>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

Documentation/video4linux/v4l2-framework.txt

+Overview of the V4L2 driver framework
+=====================================
+
+This text documents the various structures provided by the V4L2 framework and
+their relationships.
+
+
+Introduction
+------------
+
+The V4L2 drivers tend to be very complex due to the complexity of the
+hardware: most devices have multiple ICs, export multiple device nodes in
+/dev, and create also non-V4L2 devices such as DVB, ALSA, FB, I2C and input
+(IR) devices.
+
+Especially the fact that V4L2 drivers have to setup supporting ICs to
+do audio/video muxing/encoding/decoding makes it more complex than most.
+Usually these ICs are connected to the main bridge driver through one or
+more I2C busses, but other busses can also be used. Such devices are
+called 'sub-devices'.
+
+For a long time the framework was limited to the video_device struct for
+creating V4L device nodes and video_buf for handling the video buffers
+(note that this document does not discuss the video_buf framework).
+
+This meant that all drivers had to do the setup of device instances and
+connecting to sub-devices themselves. Some of this is quite complicated
+to do right and many drivers never did do it correctly.
+
+There is also a lot of common code that could never be refactored due to
+the lack of a framework.
+
+So this framework sets up the basic building blocks that all drivers
+need and this same framework should make it much easier to refactor
+common code into utility functions shared by all drivers.
+
+
+Structure of a driver
+---------------------
+
+All drivers have the following structure:
+
+1) A struct for each device instance containing the device state.
+
+2) A way of initializing and commanding sub-devices (if any).
+
+3) Creating V4L2 device nodes (/dev/videoX, /dev/vbiX, /dev/radioX and
+   /dev/vtxX) and keeping track of device-node specific data.
+
+4) Filehandle-specific structs containing per-filehandle data.
+
+This is a rough schematic of how it all relates:
+
+    device instances
+      |
+      +-sub-device instances
+      |
+      \-V4L2 device nodes
+	  |
+	  \-filehandle instances
+
+
+Structure of the framework
+--------------------------
+
+The framework closely resembles the driver structure: it has a v4l2_device
+struct for the device instance data, a v4l2_subdev struct to refer to
+sub-device instances, the video_device struct stores V4L2 device node data
+and in the future a v4l2_fh struct will keep track of filehandle instances
+(this is not yet implemented).
+
+
+struct v4l2_device
+------------------
+
+Each device instance is represented by a struct v4l2_device (v4l2-device.h).
+Very simple devices can just allocate this struct, but most of the time you
+would embed this struct inside a larger struct.
+
+You must register the device instance:
+
+	v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev);
+
+Registration will initialize the v4l2_device struct and link dev->driver_data
+to v4l2_dev. Registration will also set v4l2_dev->name to a value derived from
+dev (driver name followed by the bus_id, to be precise). You may change the
+name after registration if you want.
+
+You unregister with:
+
+	v4l2_device_unregister(struct v4l2_device *v4l2_dev);
+
+Unregistering will also automatically unregister all subdevs from the device.
+
+Sometimes you need to iterate over all devices registered by a specific
+driver. This is usually the case if multiple device drivers use the same
+hardware. E.g. the ivtvfb driver is a framebuffer driver that uses the ivtv
+hardware. The same is true for alsa drivers for example.
+
+You can iterate over all registered devices as follows:
+
+static int callback(struct device *dev, void *p)
+{
+	struct v4l2_device *v4l2_dev = dev_get_drvdata(dev);
+
+	/* test if this device was inited */
+	if (v4l2_dev == NULL)
+		return 0;
+	...
+	return 0;
+}
+
+int iterate(void *p)
+{
+	struct device_driver *drv;
+	int err;
+
+	/* Find driver 'ivtv' on the PCI bus.
+	   pci_bus_type is a global. For USB busses use usb_bus_type. */
+	drv = driver_find("ivtv", &pci_bus_type);
+	/* iterate over all ivtv device instances */
+	err = driver_for_each_device(drv, NULL, p, callback);
+	put_driver(drv);
+	return err;
+}
+
+Sometimes you need to keep a running counter of the device instance. This is
+commonly used to map a device instance to an index of a module option array.
+
+The recommended approach is as follows:
+
+static atomic_t drv_instance = ATOMIC_INIT(0);
+
+static int __devinit drv_probe(struct pci_dev *dev,
+				const struct pci_device_id *pci_id)
+{
+	...
+	state->instance = atomic_inc_return(&drv_instance) - 1;
+}
+
+
+struct v4l2_subdev
+------------------
+
+Many drivers need to communicate with sub-devices. These devices can do all
+sort of tasks, but most commonly they handle audio and/or video muxing,
+encoding or decoding. For webcams common sub-devices are sensors and camera
+controllers.
+
+Usually these are I2C devices, but not necessarily. In order to provide the
+driver with a consistent interface to these sub-devices the v4l2_subdev struct
+(v4l2-subdev.h) was created.
+
+Each sub-device driver must have a v4l2_subdev struct. This struct can be
+stand-alone for simple sub-devices or it might be embedded in a larger struct
+if more state information needs to be stored. Usually there is a low-level
+device struct (e.g. i2c_client) that contains the device data as setup
+by the kernel. It is recommended to store that pointer in the private
+data of v4l2_subdev using v4l2_set_subdevdata(). That makes it easy to go
+from a v4l2_subdev to the actual low-level bus-specific device data.
+
+You also need a way to go from the low-level struct to v4l2_subdev. For the
+common i2c_client struct the i2c_set_clientdata() call is used to store a
+v4l2_subdev pointer, for other busses you may have to use other methods.
+
+From the bridge driver perspective you load the sub-device module and somehow
+obtain the v4l2_subdev pointer. For i2c devices this is easy: you call
+i2c_get_clientdata(). For other busses something similar needs to be done.
+Helper functions exists for sub-devices on an I2C bus that do most of this
+tricky work for you.
+
+Each v4l2_subdev contains function pointers that sub-device drivers can
+implement (or leave NULL if it is not applicable). Since sub-devices can do
+so many different things and you do not want to end up with a huge ops struct
+of which only a handful of ops are commonly implemented, the function pointers
+are sorted according to category and each category has its own ops struct.
+
+The top-level ops struct contains pointers to the category ops structs, which
+may be NULL if the subdev driver does not support anything from that category.
+
+It looks like this:
+
+struct v4l2_subdev_core_ops {
+	int (*g_chip_ident)(struct v4l2_subdev *sd, struct v4l2_chip_ident *chip);
+	int (*log_status)(struct v4l2_subdev *sd);
+	int (*init)(struct v4l2_subdev *sd, u32 val);
+	...
+};
+
+struct v4l2_subdev_tuner_ops {
+	...
+};
+
+struct v4l2_subdev_audio_ops {
+	...
+};
+
+struct v4l2_subdev_video_ops {
+	...
+};
+
+struct v4l2_subdev_ops {
+	const struct v4l2_subdev_core_ops  *core;
+	const struct v4l2_subdev_tuner_ops *tuner;
+	const struct v4l2_subdev_audio_ops *audio;
+	const struct v4l2_subdev_video_ops *video;
+};
+
+The core ops are common to all subdevs, the other categories are implemented
+depending on the sub-device. E.g. a video device is unlikely to support the
+audio ops and vice versa.
+
+This setup limits the number of function pointers while still making it easy
+to add new ops and categories.
+
+A sub-device driver initializes the v4l2_subdev struct using:
+
+	v4l2_subdev_init(subdev, &ops);
+
+Afterwards you need to initialize subdev->name with a unique name and set the
+module owner. This is done for you if you use the i2c helper functions.
+
+A device (bridge) driver needs to register the v4l2_subdev with the
+v4l2_device:
+
+	int err = v4l2_device_register_subdev(device, subdev);
+
+This can fail if the subdev module disappeared before it could be registered.
+After this function was called successfully the subdev->dev field points to
+the v4l2_device.
+
+You can unregister a sub-device using:
+
+	v4l2_device_unregister_subdev(subdev);
+
+Afterwards the subdev module can be unloaded and subdev->dev == NULL.
+
+You can call an ops function either directly:
+
+	err = subdev->ops->core->g_chip_ident(subdev, &chip);
+
+but it is better and easier to use this macro:
+
+	err = v4l2_subdev_call(subdev, core, g_chip_ident, &chip);
+
+The macro will to the right NULL pointer checks and returns -ENODEV if subdev
+is NULL, -ENOIOCTLCMD if either subdev->core or subdev->core->g_chip_ident is
+NULL, or the actual result of the subdev->ops->core->g_chip_ident ops.
+
+It is also possible to call all or a subset of the sub-devices:
+
+	v4l2_device_call_all(dev, 0, core, g_chip_ident, &chip);
+
+Any subdev that does not support this ops is skipped and error results are
+ignored. If you want to check for errors use this:
+
+	err = v4l2_device_call_until_err(dev, 0, core, g_chip_ident, &chip);
+
+Any error except -ENOIOCTLCMD will exit the loop with that error. If no
+errors (except -ENOIOCTLCMD) occured, then 0 is returned.
+
+The second argument to both calls is a group ID. If 0, then all subdevs are
+called. If non-zero, then only those whose group ID match that value will
+be called. Before a bridge driver registers a subdev it can set subdev->grp_id
+to whatever value it wants (it's 0 by default). This value is owned by the
+bridge driver and the sub-device driver will never modify or use it.
+
+The group ID gives the bridge driver more control how callbacks are called.
+For example, there may be multiple audio chips on a board, each capable of
+changing the volume. But usually only one will actually be used when the
+user want to change the volume. You can set the group ID for that subdev to
+e.g. AUDIO_CONTROLLER and specify that as the group ID value when calling
+v4l2_device_call_all(). That ensures that it will only go to the subdev
+that needs it.
+
+The advantage of using v4l2_subdev is that it is a generic struct and does
+not contain any knowledge about the underlying hardware. So a driver might
+contain several subdevs that use an I2C bus, but also a subdev that is
+controlled through GPIO pins. This distinction is only relevant when setting
+up the device, but once the subdev is registered it is completely transparent.
+
+
+I2C sub-device drivers
+----------------------
+
+Since these drivers are so common, special helper functions are available to
+ease the use of these drivers (v4l2-common.h).
+
+The recommended method of adding v4l2_subdev support to an I2C driver is to
+embed the v4l2_subdev struct into the state struct that is created for each
+I2C device instance. Very simple devices have no state struct and in that case
+you can just create a v4l2_subdev directly.
+
+A typical state struct would look like this (where 'chipname' is replaced by
+the name of the chip):
+
+struct chipname_state {
+	struct v4l2_subdev sd;
+	...  /* additional state fields */
+};
+
+Initialize the v4l2_subdev struct as follows:
+
+	v4l2_i2c_subdev_init(&state->sd, client, subdev_ops);
+
+This function will fill in all the fields of v4l2_subdev and ensure that the
+v4l2_subdev and i2c_client both point to one another.
+
+You should also add a helper inline function to go from a v4l2_subdev pointer
+to a chipname_state struct:
+
+static inline struct chipname_state *to_state(struct v4l2_subdev *sd)
+{
+	return container_of(sd, struct chipname_state, sd);
+}
+
+Use this to go from the v4l2_subdev struct to the i2c_client struct:
+
+	struct i2c_client *client = v4l2_get_subdevdata(sd);
+
+And this to go from an i2c_client to a v4l2_subdev struct:
+
+	struct v4l2_subdev *sd = i2c_get_clientdata(client);
+
+Finally you need to make a command function to make driver->command()
+call the right subdev_ops functions:
+
+static int subdev_command(struct i2c_client *client, unsigned cmd, void *arg)
+{
+	return v4l2_subdev_command(i2c_get_clientdata(client), cmd, arg);
+}
+
+If driver->command is never used then you can leave this out. Eventually the
+driver->command usage should be removed from v4l.
+
+Make sure to call v4l2_device_unregister_subdev(sd) when the remove() callback
+is called. This will unregister the sub-device from the bridge driver. It is
+safe to call this even if the sub-device was never registered.
+
+
+The bridge driver also has some helper functions it can use:
+
+struct v4l2_subdev *sd = v4l2_i2c_new_subdev(adapter, "module_foo", "chipid", 0x36);
+
+This loads the given module (can be NULL if no module needs to be loaded) and
+calls i2c_new_device() with the given i2c_adapter and chip/address arguments.
+If all goes well, then it registers the subdev with the v4l2_device. It gets
+the v4l2_device by calling i2c_get_adapdata(adapter), so you should make sure
+that adapdata is set to v4l2_device when you setup the i2c_adapter in your
+driver.
+
+You can also use v4l2_i2c_new_probed_subdev() which is very similar to
+v4l2_i2c_new_subdev(), except that it has an array of possible I2C addresses
+that it should probe. Internally it calls i2c_new_probed_device().
+
+Both functions return NULL if something went wrong.
+
+
+struct video_device
+-------------------
+
+Not yet documented.

drivers/media/video/Makefile

@@ -10,7 +10,7 @@ stkwebcam-objs	:=	stk-webcam.o stk-sensor.o
 
 omap2cam-objs	:=	omap24xxcam.o omap24xxcam-dma.o
 
-videodev-objs	:=	v4l2-dev.o v4l2-ioctl.o
+videodev-objs	:=	v4l2-dev.o v4l2-ioctl.o v4l2-device.o v4l2-subdev.o
 
 obj-$(CONFIG_VIDEO_DEV) += videodev.o v4l2-compat-ioctl32.o v4l2-int-device.o
 

drivers/media/video/v4l2-device.c

+/*
+    V4L2 device support.
+
+    Copyright (C) 2008  Hans Verkuil <hverkuil@xs4all.nl>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <linux/types.h>
+#include <linux/ioctl.h>
+#include <linux/i2c.h>
+#include <linux/videodev2.h>
+#include <media/v4l2-device.h>
+
+int v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev)
+{
+	if (dev == NULL || v4l2_dev == NULL)
+		return -EINVAL;
+	/* Warn if we apparently re-register a device */
+	WARN_ON(dev_get_drvdata(dev));
+	INIT_LIST_HEAD(&v4l2_dev->subdevs);
+	spin_lock_init(&v4l2_dev->lock);
+	v4l2_dev->dev = dev;
+	snprintf(v4l2_dev->name, sizeof(v4l2_dev->name), "%s %s",
+			dev->driver->name, dev->bus_id);
+	dev_set_drvdata(dev, v4l2_dev);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(v4l2_device_register);
+
+void v4l2_device_unregister(struct v4l2_device *v4l2_dev)
+{
+	struct v4l2_subdev *sd, *next;
+
+	if (v4l2_dev == NULL || v4l2_dev->dev == NULL)
+		return;
+	dev_set_drvdata(v4l2_dev->dev, NULL);
+	/* unregister subdevs */
+	list_for_each_entry_safe(sd, next, &v4l2_dev->subdevs, list)
+		v4l2_device_unregister_subdev(sd);
+
+	v4l2_dev->dev = NULL;
+}
+EXPORT_SYMBOL_GPL(v4l2_device_unregister);
+
+int v4l2_device_register_subdev(struct v4l2_device *dev, struct v4l2_subdev *sd)
+{
+	/* Check for valid input */
+	if (dev == NULL || sd == NULL || !sd->name[0])
+		return -EINVAL;
+	/* Warn if we apparently re-register a subdev */
+	WARN_ON(sd->dev);
+	if (!try_module_get(sd->owner))
+		return -ENODEV;
+	sd->dev = dev;
+	spin_lock(&dev->lock);
+	list_add_tail(&sd->list, &dev->subdevs);
+	spin_unlock(&dev->lock);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(v4l2_device_register_subdev);
+
+void v4l2_device_unregister_subdev(struct v4l2_subdev *sd)
+{
+	/* return if it isn't registered */
+	if (sd == NULL || sd->dev == NULL)
+		return;
+	spin_lock(&sd->dev->lock);
+	list_del(&sd->list);
+	spin_unlock(&sd->dev->lock);
+	sd->dev = NULL;
+	module_put(sd->owner);
+}
+EXPORT_SYMBOL_GPL(v4l2_device_unregister_subdev);

drivers/media/video/v4l2-subdev.c

+/*
+    V4L2 sub-device support.
+
+    Copyright (C) 2008  Hans Verkuil <hverkuil@xs4all.nl>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <linux/types.h>
+#include <linux/ioctl.h>
+#include <linux/i2c.h>
+#include <linux/videodev2.h>
+#include <media/v4l2-subdev.h>
+
+int v4l2_subdev_command(struct v4l2_subdev *sd, unsigned cmd, void *arg)
+{
+	switch (cmd) {
+	case VIDIOC_QUERYCTRL:
+		return v4l2_subdev_call(sd, core, querymenu, arg);
+	case VIDIOC_G_CTRL:
+		return v4l2_subdev_call(sd, core, g_ctrl, arg);
+	case VIDIOC_S_CTRL:
+		return v4l2_subdev_call(sd, core, s_ctrl, arg);
+	case VIDIOC_QUERYMENU:
+		return v4l2_subdev_call(sd, core, queryctrl, arg);
+	case VIDIOC_LOG_STATUS:
+		return v4l2_subdev_call(sd, core, log_status);
+	case VIDIOC_G_CHIP_IDENT:
+		return v4l2_subdev_call(sd, core, g_chip_ident, arg);
+	case VIDIOC_INT_S_STANDBY:
+		return v4l2_subdev_call(sd, core, s_standby, *(u32 *)arg);
+	case VIDIOC_INT_RESET:
+		return v4l2_subdev_call(sd, core, reset, *(u32 *)arg);
+	case VIDIOC_INT_S_GPIO:
+		return v4l2_subdev_call(sd, core, s_gpio, *(u32 *)arg);
+	case VIDIOC_INT_INIT:
+		return v4l2_subdev_call(sd, core, init, *(u32 *)arg);
+#ifdef CONFIG_VIDEO_ADV_DEBUG
+	case VIDIOC_DBG_G_REGISTER:
+		return v4l2_subdev_call(sd, core, g_register, arg);
+	case VIDIOC_DBG_S_REGISTER:
+		return v4l2_subdev_call(sd, core, s_register, arg);
+#endif
+
+	case VIDIOC_INT_S_TUNER_MODE:
+		return v4l2_subdev_call(sd, tuner, s_mode, *(enum v4l2_tuner_type *)arg);
+	case AUDC_SET_RADIO:
+		return v4l2_subdev_call(sd, tuner, s_radio);
+	case VIDIOC_S_TUNER:
+		return v4l2_subdev_call(sd, tuner, s_tuner, arg);
+	case VIDIOC_G_TUNER:
+		return v4l2_subdev_call(sd, tuner, g_tuner, arg);
+	case VIDIOC_S_STD:
+		return v4l2_subdev_call(sd, tuner, s_std, *(v4l2_std_id *)arg);
+	case VIDIOC_S_FREQUENCY:
+		return v4l2_subdev_call(sd, tuner, s_frequency, arg);
+	case VIDIOC_G_FREQUENCY:
+		return v4l2_subdev_call(sd, tuner, g_frequency, arg);
+	case TUNER_SET_TYPE_ADDR:
+		return v4l2_subdev_call(sd, tuner, s_type_addr, arg);
+	case TUNER_SET_CONFIG:
+		return v4l2_subdev_call(sd, tuner, s_config, arg);
+
+	case VIDIOC_INT_AUDIO_CLOCK_FREQ:
+		return v4l2_subdev_call(sd, audio, s_clock_freq, *(u32 *)arg);
+	case VIDIOC_INT_S_AUDIO_ROUTING:
+		return v4l2_subdev_call(sd, audio, s_routing, arg);
+	case VIDIOC_INT_I2S_CLOCK_FREQ:
+		return v4l2_subdev_call(sd, audio, s_i2s_clock_freq, *(u32 *)arg);
+
+	case VIDIOC_INT_S_VIDEO_ROUTING:
+		return v4l2_subdev_call(sd, video, s_routing, arg);
+	case VIDIOC_INT_S_CRYSTAL_FREQ:
+		return v4l2_subdev_call(sd, video, s_crystal_freq, arg);
+	case VIDIOC_INT_DECODE_VBI_LINE:
+		return v4l2_subdev_call(sd, video, decode_vbi_line, arg);
+	case VIDIOC_INT_S_VBI_DATA:
+		return v4l2_subdev_call(sd, video, s_vbi_data, arg);
+	case VIDIOC_INT_G_VBI_DATA:
+		return v4l2_subdev_call(sd, video, g_vbi_data, arg);
+	case VIDIOC_S_FMT:
+		return v4l2_subdev_call(sd, video, s_fmt, arg);
+	case VIDIOC_G_FMT:
+		return v4l2_subdev_call(sd, video, g_fmt, arg);
+	case VIDIOC_INT_S_STD_OUTPUT:
+		return v4l2_subdev_call(sd, video, s_std_output, *(v4l2_std_id *)arg);
+	case VIDIOC_STREAMON:
+		return v4l2_subdev_call(sd, video, s_stream, 1);
+	case VIDIOC_STREAMOFF:
+		return v4l2_subdev_call(sd, video, s_stream, 0);
+
+	default:
+		return v4l2_subdev_call(sd, core, ioctl, cmd, arg);
+	}
+}
+EXPORT_SYMBOL_GPL(v4l2_subdev_command);

include/media/v4l2-device.h

+/*
+    V4L2 device support header.
+
+    Copyright (C) 2008  Hans Verkuil <hverkuil@xs4all.nl>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#ifndef _V4L2_DEVICE_H
+#define _V4L2_DEVICE_H
+
+#include <media/v4l2-subdev.h>
+
+/* Each instance of a V4L2 device should create the v4l2_device struct,
+   either stand-alone or embedded in a larger struct.
+
+   It allows easy access to sub-devices (see v4l2-subdev.h) and provides
+   basic V4L2 device-level support.
+ */
+
+#define V4L2_DEVICE_NAME_SIZE (BUS_ID_SIZE + 16)
+
+struct v4l2_device {
+	/* dev->driver_data points to this struct */
+	struct device *dev;
+	/* used to keep track of the registered subdevs */
+	struct list_head subdevs;
+	/* lock this struct; can be used by the driver as well if this
+	   struct is embedded into a larger struct. */
+	spinlock_t lock;
+	/* unique device name, by default the driver name + bus ID */
+	char name[V4L2_DEVICE_NAME_SIZE];
+};
+
+/* Initialize v4l2_dev and make dev->driver_data point to v4l2_dev */
+int __must_check v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev);
+/* Set v4l2_dev->dev->driver_data to NULL and unregister all sub-devices */
+void v4l2_device_unregister(struct v4l2_device *v4l2_dev);
+
+/* Register a subdev with a v4l2 device. While registered the subdev module
+   is marked as in-use. An error is returned if the module is no longer
+   loaded when you attempt to register it. */
+int __must_check v4l2_device_register_subdev(struct v4l2_device *dev, struct v4l2_subdev *sd);
+/* Unregister a subdev with a v4l2 device. Can also be called if the subdev
+   wasn't registered. In that case it will do nothing. */
+void v4l2_device_unregister_subdev(struct v4l2_subdev *sd);
+
+/* Iterate over all subdevs. */
+#define v4l2_device_for_each_subdev(sd, dev)				\
+	list_for_each_entry(sd, &(dev)->subdevs, list)
+
+/* Call the specified callback for all subdevs matching the condition.
+   Ignore any errors. Note that you cannot add or delete a subdev
+   while walking the subdevs list. */
+#define __v4l2_device_call_subdevs(dev, cond, o, f, args...) 		\
+	do { 								\
+		struct v4l2_subdev *sd; 				\
+									\
+		list_for_each_entry(sd, &(dev)->subdevs, list)   	\
+			if ((cond) && sd->ops->o && sd->ops->o->f) 	\
+				sd->ops->o->f(sd , ##args); 		\
+	} while (0)
+
+/* Call the specified callback for all subdevs matching the condition.
+   If the callback returns an error other than 0 or -ENOIOCTLCMD, then
+   return with that error code. Note that you cannot add or delete a
+   subdev while walking the subdevs list. */
+#define __v4l2_device_call_subdevs_until_err(dev, cond, o, f, args...)  \
+({ 									\
+	struct v4l2_subdev *sd; 					\
+	int err = 0; 							\
+									\
+	list_for_each_entry(sd, &(dev)->subdevs, list) { 		\
+		if ((cond) && sd->ops->o && sd->ops->o->f) 		\
+			err = sd->ops->o->f(sd , ##args); 		\
+		if (err && err != -ENOIOCTLCMD)				\
+			break; 						\
+	} 								\
+	(err == -ENOIOCTLCMD) ? 0 : err; 				\
+})
+
+/* Call the specified callback for all subdevs matching grp_id (if 0, then
+   match them all). Ignore any errors. Note that you cannot add or delete
+   a subdev while walking the subdevs list. */
+#define v4l2_device_call_all(dev, grp_id, o, f, args...) 		\
+	__v4l2_device_call_subdevs(dev, 				\
+			!(grp_id) || sd->grp_id == (grp_id), o, f , ##args)
+
+/* Call the specified callback for all subdevs matching grp_id (if 0, then
+   match them all). If the callback returns an error other than 0 or
+   -ENOIOCTLCMD, then return with that error code. Note that you cannot
+   add or delete a subdev while walking the subdevs list. */
+#define v4l2_device_call_until_err(dev, grp_id, o, f, args...) 		\
+	__v4l2_device_call_subdevs_until_err(dev,			\
+		       !(grp_id) || sd->grp_id == (grp_id), o, f , ##args)
+
+#endif

include/media/v4l2-subdev.h

+/*
+    V4L2 sub-device support header.
+
+    Copyright (C) 2008  Hans Verkuil <hverkuil@xs4all.nl>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#ifndef _V4L2_SUBDEV_H
+#define _V4L2_SUBDEV_H
+
+#include <media/v4l2-common.h>
+
+struct v4l2_device;
+struct v4l2_subdev;
+struct tuner_setup;
+
+/* Sub-devices are devices that are connected somehow to the main bridge
+   device. These devices are usually audio/video muxers/encoders/decoders or
+   sensors and webcam controllers.
+
+   Usually these devices are controlled through an i2c bus, but other busses
+   may also be used.
+
+   The v4l2_subdev struct provides a way of accessing these devices in a
+   generic manner. Most operations that these sub-devices support fall in
+   a few categories: core ops, audio ops, video ops and tuner ops.
+
+   More categories can be added if needed, although this should remain a
+   limited set (no more than approx. 8 categories).
+
+   Each category has its own set of ops that subdev drivers can implement.
+
+   A subdev driver can leave the pointer to the category ops NULL if
+   it does not implement them (e.g. an audio subdev will generally not
+   implement the video category ops). The exception is the core category:
+   this must always be present.
+
+   These ops are all used internally so it is no problem to change, remove
+   or add ops or move ops from one to another category. Currently these
+   ops are based on the original ioctls, but since ops are not limited to
+   one argument there is room for improvement here once all i2c subdev
+   drivers are converted to use these ops.
+ */
+
+/* Core ops: it is highly recommended to implement at least these ops:
+
+   g_chip_ident
+   log_status
+   g_register
+   s_register
+
+   This provides basic debugging support.
+
+   The ioctl ops is meant for generic ioctl-like commands. Depending on
+   the use-case it might be better to use subdev-specific ops (currently
+   not yet implemented) since ops provide proper type-checking.
+ */
+struct v4l2_subdev_core_ops {
+	int (*g_chip_ident)(struct v4l2_subdev *sd, struct v4l2_chip_ident *chip);
+	int (*log_status)(struct v4l2_subdev *sd);
+	int (*init)(struct v4l2_subdev *sd, u32 val);
+	int (*s_standby)(struct v4l2_subdev *sd, u32 standby);
+	int (*reset)(struct v4l2_subdev *sd, u32 val);
+	int (*s_gpio)(struct v4l2_subdev *sd, u32 val);
+	int (*queryctrl)(struct v4l2_subdev *sd, struct v4l2_queryctrl *qc);
+	int (*g_ctrl)(struct v4l2_subdev *sd, struct v4l2_control *ctrl);
+	int (*s_ctrl)(struct v4l2_subdev *sd, struct v4l2_control *ctrl);
+	int (*querymenu)(struct v4l2_subdev *sd, struct v4l2_querymenu *qm);
+	int (*ioctl)(struct v4l2_subdev *sd, int cmd, void *arg);
+#ifdef CONFIG_VIDEO_ADV_DEBUG
+	int (*g_register)(struct v4l2_subdev *sd, struct v4l2_register *reg);
+	int (*s_register)(struct v4l2_subdev *sd, struct v4l2_register *reg);
+#endif
+};
+
+struct v4l2_subdev_tuner_ops {
+	int (*s_mode)(struct v4l2_subdev *sd, enum v4l2_tuner_type);
+	int (*s_radio)(struct v4l2_subdev *sd);
+	int (*s_frequency)(struct v4l2_subdev *sd, struct v4l2_frequency *freq);
+	int (*g_frequency)(struct v4l2_subdev *sd, struct v4l2_frequency *freq);
+	int (*g_tuner)(struct v4l2_subdev *sd, struct v4l2_tuner *vt);
+	int (*s_tuner)(struct v4l2_subdev *sd, struct v4l2_tuner *vt);
+	int (*s_std)(struct v4l2_subdev *sd, v4l2_std_id norm);
+	int (*s_type_addr)(struct v4l2_subdev *sd, struct tuner_setup *type);
+	int (*s_config)(struct v4l2_subdev *sd, const struct v4l2_priv_tun_config *config);
+};
+
+struct v4l2_subdev_audio_ops {
+	int (*s_clock_freq)(struct v4l2_subdev *sd, u32 freq);
+	int (*s_i2s_clock_freq)(struct v4l2_subdev *sd, u32 freq);
+	int (*s_routing)(struct v4l2_subdev *sd, const struct v4l2_routing *route);
+};
+
+struct v4l2_subdev_video_ops {
+	int (*s_routing)(struct v4l2_subdev *sd, const struct v4l2_routing *route);
+	int (*s_crystal_freq)(struct v4l2_subdev *sd, struct v4l2_crystal_freq *freq);
+	int (*decode_vbi_line)(struct v4l2_subdev *sd, struct v4l2_decode_vbi_line *vbi_line);
+	int (*s_vbi_data)(struct v4l2_subdev *sd, const struct v4l2_sliced_vbi_data *vbi_data);
+	int (*g_vbi_data)(struct v4l2_subdev *sd, struct v4l2_sliced_vbi_data *vbi_data);
+	int (*s_std_output)(struct v4l2_subdev *sd, v4l2_std_id std);
+	int (*s_stream)(struct v4l2_subdev *sd, int enable);
+	int (*s_fmt)(struct v4l2_subdev *sd, struct v4l2_format *fmt);
+	int (*g_fmt)(struct v4l2_subdev *sd, struct v4l2_format *fmt);
+};
+
+struct v4l2_subdev_ops {
+	const struct v4l2_subdev_core_ops  *core;
+	const struct v4l2_subdev_tuner_ops *tuner;
+	const struct v4l2_subdev_audio_ops *audio;
+	const struct v4l2_subdev_video_ops *video;
+};
+
+#define V4L2_SUBDEV_NAME_SIZE 32
+
+/* Each instance of a subdev driver should create this struct, either
+   stand-alone or embedded in a larger struct.
+ */
+struct v4l2_subdev {
+	struct list_head list;
+	struct module *owner;
+	struct v4l2_device *dev;
+	const struct v4l2_subdev_ops *ops;
+	/* name must be unique */
+	char name[V4L2_SUBDEV_NAME_SIZE];
+	/* can be used to group similar subdevs, value is driver-specific */
+	u32 grp_id;
+	/* pointer to private data */
+	void *priv;
+};
+
+static inline void v4l2_set_subdevdata(struct v4l2_subdev *sd, void *p)
+{
+	sd->priv = p;
+}
+
+static inline void *v4l2_get_subdevdata(const struct v4l2_subdev *sd)
+{
+	return sd->priv;
+}
+
+/* Convert an ioctl-type command to the proper v4l2_subdev_ops function call.
+   This is used by subdev modules that can be called by both old-style ioctl
+   commands and through the v4l2_subdev_ops.
+
+   The ioctl API of the subdev driver can call this function to call the
+   right ops based on the ioctl cmd and arg.
+
+   Once all subdev drivers have been converted and all drivers no longer
+   use the ioctl interface, then this function can be removed.
+ */
+int v4l2_subdev_command(struct v4l2_subdev *sd, unsigned cmd, void *arg);
+
+static inline void v4l2_subdev_init(struct v4l2_subdev *sd,
+					const struct v4l2_subdev_ops *ops)
+{
+	INIT_LIST_HEAD(&sd->list);
+	/* ops->core MUST be set */
+	BUG_ON(!ops || !ops->core);
+	sd->ops = ops;
+	sd->dev = NULL;
+	sd->name[0] = '\0';
+	sd->grp_id = 0;
+	sd->priv = NULL;
+}
+
+/* Call an ops of a v4l2_subdev, doing the right checks against
+   NULL pointers.
+
+   Example: err = v4l2_subdev_call(sd, core, g_chip_ident, &chip);
+ */
+#define v4l2_subdev_call(sd, o, f, args...)				\
+	(!(sd) ? -ENODEV : (((sd) && (sd)->ops->o && (sd)->ops->o->f) ?	\
+		(sd)->ops->o->f((sd) , ##args) : -ENOIOCTLCMD))
+
+#endif