Subject: Re: [PATCH v2] v4l2_device/v4l2_subdev: final (?) version
From: Andy Walls <awalls@radix.net>
To: Hans Verkuil <hverkuil@xs4all.nl>
Cc: Linux and Kernel Video <video4linux-list@redhat.com>,
       "linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>,
       "davinci-linux-open-source@linux.davincidsp.com" 
	<davinci-linux-open-source@linux.davincidsp.com>,
       linux-kernel@vger.kernel.org
In-Reply-To: <200811291852.41794.hverkuil@xs4all.nl>
References: <200811291852.41794.hverkuil@xs4all.nl>
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Date: Sat, 29 Nov 2008 18:31:38 -0500
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On Sat, 2008-11-29 at 18:52 +0100, Hans Verkuil wrote:
> Hi all,
> 
> This is hopefully the final version. All earlier comments have been
> incorporated into this patch. I also made a new change: the mutex has been
> replaced by a spinlock and I no longer lock when walking the list of subdevs.
> 
> So the assumption is that subdevs only added during initialization of the
> device and removed during the destruction of the device, and not in between.
> I cannot think of any reason why this you would want to do this, but should
> this ever happen then the list should be replaced by a klist. I consider
> this overkill, esp. since walking the subdev list should be as fast as
> possible.

I don't have a problem with not locking during a list walk as long as
you can ensure the register and unregister calls can't happen in the
middle of a walk.  I haven't taken a hard look to see if this is the
case.  I'd imagine a walk while registration is going on is the only
case that has a remote chance of happening.

Although I think I've just answered my own next question I'll ask
anyway: why are register & unregister such time critical operations that
we have to spin instead of risk sleeping in a mutex?  To greatly reduce
the probability a walk happens while registering?  If that's the case it
sounds like we're knowingly building in a race. 

This comment kind of bugged me too:

>/* Iterate over all subdevs. The next item is prefetched, so you can
> +   delete the current item if necessary. */
> +#define v4l2_device_for_each_subdev(sd, dev)

It implies it's safe to remove things from the list that we're not
locking.

I can appreciate the desire for being able to walk the list and issue
commands to various subdevs with high concurrency.  I know spinlocks are
optimized for the common case of the lock being available (well at least
the underlying __raw_spin_lock() is optimized, if preemption is enabled
there's a little overhead added).  So they give the safety with a minor
penalty at the micro level, but kill concurrency of common operations at
the macro level.

So how about a rwlock_t and using read_lock() and write_lock(), locks
that provide safety and allow high concurrency at the macro level?  I
don't know if there's an analog of a read/write mutex.

Did I totally miss the concept?

Regards,
Andy

> 
> The full tree which includes the i2c module and ivtv conversion as well can
> be accessed here: http://linuxtv.org/hg/~hverkuil/v4l-dvb-ng
> 
> Regards,
> 
> 	Hans
> 
> # HG changeset patch
> # User Hans Verkuil <hverkuil@xs4all.nl>
> # Date 1227979357 -3600
> # Node ID 719584d5989d93b7ccb3de54155cbab9e6b06526
> # Parent  7100e78482d70ee9acf90f2c15848f6002f89b7d
> v4l2: add v4l2_device and v4l2_subdev structs to the v4l2 framework.
> 
> From: Hans Verkuil <hverkuil@xs4all.nl>
> 
> 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).
> 
> Priority: normal
> 
> Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@skynet.be>
> Reviewed-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> Reviewed-by: Andy Walls <awalls@radix.net>
> 
> diff -r 7100e78482d7 -r 719584d5989d linux/Documentation/video4linux/v4l2-framework.txt
> --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
> +++ b/linux/Documentation/video4linux/v4l2-framework.txt	Sat Nov 29 18:22:37 2008 +0100
> @@ -0,0 +1,362 @@
> +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.
> diff -r 7100e78482d7 -r 719584d5989d linux/drivers/media/video/Makefile
> --- a/linux/drivers/media/video/Makefile	Sat Nov 29 00:46:43 2008 -0200
> +++ b/linux/drivers/media/video/Makefile	Sat Nov 29 18:22:37 2008 +0100
> @@ -8,7 +8,7 @@
>  
>  stkwebcam-objs	:=	stk-webcam.o stk-sensor.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
>  
> diff -r 7100e78482d7 -r 719584d5989d linux/drivers/media/video/v4l2-device.c
> --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
> +++ b/linux/drivers/media/video/v4l2-device.c	Sat Nov 29 18:22:37 2008 +0100
> @@ -0,0 +1,80 @@
> +/*
> +    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>
> +
> +void v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev)
> +{
> +	BUG_ON(!dev || !v4l2_dev || 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);
> +}
> +EXPORT_SYMBOL(v4l2_device_register);
> +
> +void v4l2_device_unregister(struct v4l2_device *v4l2_dev)
> +{
> +	struct v4l2_subdev *sd, *next;
> +
> +	BUG_ON(!v4l2_dev || !v4l2_dev->dev || !dev_get_drvdata(v4l2_dev->dev));
> +	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(v4l2_device_unregister);
> +
> +int v4l2_device_register_subdev(struct v4l2_device *dev, struct v4l2_subdev *sd)
> +{
> +	/* Check that sd->dev is not set and that the subdev's name is
> +	   filled in. */
> +	BUG_ON(!dev || !sd || sd->dev || !sd->name[0]);
> +	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(v4l2_device_register_subdev);
> +
> +void v4l2_device_unregister_subdev(struct v4l2_subdev *sd)
> +{
> +	BUG_ON(!sd);
> +	/* return if it isn't registered */
> +	if (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(v4l2_device_unregister_subdev);
> diff -r 7100e78482d7 -r 719584d5989d linux/drivers/media/video/v4l2-subdev.c
> --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
> +++ b/linux/drivers/media/video/v4l2-subdev.c	Sat Nov 29 18:22:37 2008 +0100
> @@ -0,0 +1,108 @@
> +/*
> +    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(v4l2_subdev_command);
> diff -r 7100e78482d7 -r 719584d5989d linux/include/media/v4l2-device.h
> --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
> +++ b/linux/include/media/v4l2-device.h	Sat Nov 29 18:22:37 2008 +0100
> @@ -0,0 +1,109 @@
> +/*
> +    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 */
> +void 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 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. The next item is prefetched, so you can
> +   delete the current item if necessary. */
> +#define v4l2_device_for_each_subdev(sd, dev)				\
> +	for (sd = list_entry((dev)->subdevs.next, typeof(*sd), list); 	\
> +		prefetch(sd->list.next), &sd->list != &(dev)->subdevs; 	\
> +	     sd = list_entry(sd->list.next, typeof(*sd), list))
> +
> +/* Call the specified callback for all subdevs matching the condition.
> +   Ignore any errors. */
> +#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. */
> +#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. */
> +#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. */
> +#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
> diff -r 7100e78482d7 -r 719584d5989d linux/include/media/v4l2-subdev.h
> --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
> +++ b/linux/include/media/v4l2-subdev.h	Sat Nov 29 18:22:37 2008 +0100
> @@ -0,0 +1,188 @@
> +/*
> +    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
> 
> 

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