Commit cf4b9211 authored by Laurent Pinchart's avatar Laurent Pinchart Committed by Mauro Carvalho Chehab
Browse files

[media] media: Media device node support 



The media_devnode structure provides support for registering and
unregistering character devices using a dynamic major number. Reference
counting is handled internally, making device drivers easier to write
without having to solve the open/disconnect race condition issue over
and over again.

The code is based on video/v4l2-dev.c.

[mchehab@redhat.com: Remove linux/smp_lock.h include to not break compilation on bisect]
Signed-off-by: default avatarLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: default avatarHans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@redhat.com>
parent 02adb1cc

drivers/media/Kconfig

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@@ -13,6 +13,19 @@ if MEDIA_SUPPORT 


comment "Multimedia core support"



#

# Media controller

#



config MEDIA_CONTROLLER

	bool "Media Controller API (EXPERIMENTAL)"

	depends on EXPERIMENTAL

	---help---

	  Enable the media controller API used to query media devices internal

	  topology and configure it dynamically.



	  This API is mostly used by camera interfaces in embedded platforms.



#

# V4L core and enabled API's

#

drivers/media/Makefile

+6 −0
Original line number Diff line number Diff line
@@ -2,6 +2,12 @@ 
# Makefile for the kernel multimedia device drivers.

#



media-objs	:= media-devnode.o



ifeq ($(CONFIG_MEDIA_CONTROLLER),y)

  obj-$(CONFIG_MEDIA_SUPPORT) += media.o

endif



obj-y += common/ rc/ video/



obj-$(CONFIG_VIDEO_DEV) += radio/

drivers/media/media-devnode.c

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/*

 * Media device node

 *

 * Copyright (C) 2010 Nokia Corporation

 *

 * Based on drivers/media/video/v4l2_dev.c code authored by

 *	Mauro Carvalho Chehab <mchehab@infradead.org> (version 2)

 *	Alan Cox, <alan@lxorguk.ukuu.org.uk> (version 1)

 *

 * Contacts: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

 *	     Sakari Ailus <sakari.ailus@iki.fi>

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 *

 * 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

 *

 * --

 *

 * Generic media device node infrastructure to register and unregister

 * character devices using a dynamic major number and proper reference

 * counting.

 */



#include <linux/errno.h>

#include <linux/init.h>

#include <linux/module.h>

#include <linux/kernel.h>

#include <linux/kmod.h>

#include <linux/slab.h>

#include <linux/mm.h>

#include <linux/string.h>

#include <linux/types.h>

#include <linux/uaccess.h>

#include <asm/system.h>



#include <media/media-devnode.h>



#define MEDIA_NUM_DEVICES	256

#define MEDIA_NAME		"media"



static dev_t media_dev_t;



/*

 *	Active devices

 */

static DEFINE_MUTEX(media_devnode_lock);

static DECLARE_BITMAP(media_devnode_nums, MEDIA_NUM_DEVICES);



/* Called when the last user of the media device exits. */

static void media_devnode_release(struct device *cd)

{

	struct media_devnode *mdev = to_media_devnode(cd);



	mutex_lock(&media_devnode_lock);



	/* Delete the cdev on this minor as well */

	cdev_del(&mdev->cdev);



	/* Mark device node number as free */

	clear_bit(mdev->minor, media_devnode_nums);



	mutex_unlock(&media_devnode_lock);



	/* Release media_devnode and perform other cleanups as needed. */

	if (mdev->release)

		mdev->release(mdev);

}



static struct bus_type media_bus_type = {

	.name = MEDIA_NAME,

};



static ssize_t media_read(struct file *filp, char __user *buf,

		size_t sz, loff_t *off)

{

	struct media_devnode *mdev = media_devnode_data(filp);



	if (!mdev->fops->read)

		return -EINVAL;

	if (!media_devnode_is_registered(mdev))

		return -EIO;

	return mdev->fops->read(filp, buf, sz, off);

}



static ssize_t media_write(struct file *filp, const char __user *buf,

		size_t sz, loff_t *off)

{

	struct media_devnode *mdev = media_devnode_data(filp);



	if (!mdev->fops->write)

		return -EINVAL;

	if (!media_devnode_is_registered(mdev))

		return -EIO;

	return mdev->fops->write(filp, buf, sz, off);

}



static unsigned int media_poll(struct file *filp,

			       struct poll_table_struct *poll)

{

	struct media_devnode *mdev = media_devnode_data(filp);



	if (!media_devnode_is_registered(mdev))

		return POLLERR | POLLHUP;

	if (!mdev->fops->poll)

		return DEFAULT_POLLMASK;

	return mdev->fops->poll(filp, poll);

}



static long media_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)

{

	struct media_devnode *mdev = media_devnode_data(filp);



	if (!mdev->fops->ioctl)

		return -ENOTTY;



	if (!media_devnode_is_registered(mdev))

		return -EIO;



	return mdev->fops->ioctl(filp, cmd, arg);

}



/* Override for the open function */

static int media_open(struct inode *inode, struct file *filp)

{

	struct media_devnode *mdev;

	int ret;



	/* Check if the media device is available. This needs to be done with

	 * the media_devnode_lock held to prevent an open/unregister race:

	 * without the lock, the device could be unregistered and freed between

	 * the media_devnode_is_registered() and get_device() calls, leading to

	 * a crash.

	 */

	mutex_lock(&media_devnode_lock);

	mdev = container_of(inode->i_cdev, struct media_devnode, cdev);

	/* return ENXIO if the media device has been removed

	   already or if it is not registered anymore. */

	if (!media_devnode_is_registered(mdev)) {

		mutex_unlock(&media_devnode_lock);

		return -ENXIO;

	}

	/* and increase the device refcount */

	get_device(&mdev->dev);

	mutex_unlock(&media_devnode_lock);



	filp->private_data = mdev;



	if (mdev->fops->open) {

		ret = mdev->fops->open(filp);

		if (ret) {

			put_device(&mdev->dev);

			return ret;

		}

	}



	return 0;

}



/* Override for the release function */

static int media_release(struct inode *inode, struct file *filp)

{

	struct media_devnode *mdev = media_devnode_data(filp);

	int ret = 0;



	if (mdev->fops->release)

		mdev->fops->release(filp);



	/* decrease the refcount unconditionally since the release()

	   return value is ignored. */

	put_device(&mdev->dev);

	filp->private_data = NULL;

	return ret;

}



static const struct file_operations media_devnode_fops = {

	.owner = THIS_MODULE,

	.read = media_read,

	.write = media_write,

	.open = media_open,

	.unlocked_ioctl = media_ioctl,

	.release = media_release,

	.poll = media_poll,

	.llseek = no_llseek,

};



/**

 * media_devnode_register - register a media device node

 * @mdev: media device node structure we want to register

 *

 * The registration code assigns minor numbers and registers the new device node

 * with the kernel. An error is returned if no free minor number can be found,

 * or if the registration of the device node fails.

 *

 * Zero is returned on success.

 *

 * Note that if the media_devnode_register call fails, the release() callback of

 * the media_devnode structure is *not* called, so the caller is responsible for

 * freeing any data.

 */

int __must_check media_devnode_register(struct media_devnode *mdev)

{

	int minor;

	int ret;



	/* Part 1: Find a free minor number */

	mutex_lock(&media_devnode_lock);

	minor = find_next_zero_bit(media_devnode_nums, 0, MEDIA_NUM_DEVICES);

	if (minor == MEDIA_NUM_DEVICES) {

		mutex_unlock(&media_devnode_lock);

		printk(KERN_ERR "could not get a free minor\n");

		return -ENFILE;

	}



	set_bit(mdev->minor, media_devnode_nums);

	mutex_unlock(&media_devnode_lock);



	mdev->minor = minor;



	/* Part 2: Initialize and register the character device */

	cdev_init(&mdev->cdev, &media_devnode_fops);

	mdev->cdev.owner = mdev->fops->owner;



	ret = cdev_add(&mdev->cdev, MKDEV(MAJOR(media_dev_t), mdev->minor), 1);

	if (ret < 0) {

		printk(KERN_ERR "%s: cdev_add failed\n", __func__);

		goto error;

	}



	/* Part 3: Register the media device */

	mdev->dev.bus = &media_bus_type;

	mdev->dev.devt = MKDEV(MAJOR(media_dev_t), mdev->minor);

	mdev->dev.release = media_devnode_release;

	if (mdev->parent)

		mdev->dev.parent = mdev->parent;

	dev_set_name(&mdev->dev, "media%d", mdev->minor);

	ret = device_register(&mdev->dev);

	if (ret < 0) {

		printk(KERN_ERR "%s: device_register failed\n", __func__);

		goto error;

	}



	/* Part 4: Activate this minor. The char device can now be used. */

	set_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);



	return 0;



error:

	cdev_del(&mdev->cdev);

	clear_bit(mdev->minor, media_devnode_nums);

	return ret;

}



/**

 * media_devnode_unregister - unregister a media device node

 * @mdev: the device node to unregister

 *

 * This unregisters the passed device. Future open calls will be met with

 * errors.

 *

 * This function can safely be called if the device node has never been

 * registered or has already been unregistered.

 */

void media_devnode_unregister(struct media_devnode *mdev)

{

	/* Check if mdev was ever registered at all */

	if (!media_devnode_is_registered(mdev))

		return;



	mutex_lock(&media_devnode_lock);

	clear_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);

	mutex_unlock(&media_devnode_lock);

	device_unregister(&mdev->dev);

}



/*

 *	Initialise media for linux

 */

static int __init media_devnode_init(void)

{

	int ret;



	printk(KERN_INFO "Linux media interface: v0.10\n");

	ret = alloc_chrdev_region(&media_dev_t, 0, MEDIA_NUM_DEVICES,

				  MEDIA_NAME);

	if (ret < 0) {

		printk(KERN_WARNING "media: unable to allocate major\n");

		return ret;

	}



	ret = bus_register(&media_bus_type);

	if (ret < 0) {

		unregister_chrdev_region(media_dev_t, MEDIA_NUM_DEVICES);

		printk(KERN_WARNING "media: bus_register failed\n");

		return -EIO;

	}



	return 0;

}



static void __exit media_devnode_exit(void)

{

	bus_unregister(&media_bus_type);

	unregister_chrdev_region(media_dev_t, MEDIA_NUM_DEVICES);

}



module_init(media_devnode_init)

module_exit(media_devnode_exit)



MODULE_AUTHOR("Laurent Pinchart <laurent.pinchart@ideasonboard.com>");

MODULE_DESCRIPTION("Device node registration for media drivers");

MODULE_LICENSE("GPL");

include/media/media-devnode.h

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Original line number Diff line number Diff line 
/*

 * Media device node

 *

 * Copyright (C) 2010 Nokia Corporation

 *

 * Contacts: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

 *	     Sakari Ailus <sakari.ailus@iki.fi>

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 *

 * 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

 *

 * --

 *

 * Common functions for media-related drivers to register and unregister media

 * device nodes.

 */



#ifndef _MEDIA_DEVNODE_H

#define _MEDIA_DEVNODE_H



#include <linux/poll.h>

#include <linux/fs.h>

#include <linux/device.h>

#include <linux/cdev.h>



/*

 * Flag to mark the media_devnode struct as registered. Drivers must not touch

 * this flag directly, it will be set and cleared by media_devnode_register and

 * media_devnode_unregister.

 */

#define MEDIA_FLAG_REGISTERED	0



struct media_file_operations {

	struct module *owner;

	ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);

	ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);

	unsigned int (*poll) (struct file *, struct poll_table_struct *);

	long (*ioctl) (struct file *, unsigned int, unsigned long);

	int (*open) (struct file *);

	int (*release) (struct file *);

};



/**

 * struct media_devnode - Media device node

 * @parent:	parent device

 * @minor:	device node minor number

 * @flags:	flags, combination of the MEDIA_FLAG_* constants

 *

 * This structure represents a media-related device node.

 *

 * The @parent is a physical device. It must be set by core or device drivers

 * before registering the node.

 */

struct media_devnode {

	/* device ops */

	const struct media_file_operations *fops;



	/* sysfs */

	struct device dev;		/* media device */

	struct cdev cdev;		/* character device */

	struct device *parent;		/* device parent */



	/* device info */

	int minor;

	unsigned long flags;		/* Use bitops to access flags */



	/* callbacks */

	void (*release)(struct media_devnode *mdev);

};



/* dev to media_devnode */

#define to_media_devnode(cd) container_of(cd, struct media_devnode, dev)



int __must_check media_devnode_register(struct media_devnode *mdev);

void media_devnode_unregister(struct media_devnode *mdev);



static inline struct media_devnode *media_devnode_data(struct file *filp)

{

	return filp->private_data;

}



static inline int media_devnode_is_registered(struct media_devnode *mdev)

{

	return test_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);

}



#endif /* _MEDIA_DEVNODE_H */

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