drm/display/drm_dp_aux_dev.c

/*
 * Copyright © 2015 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 * Authors:
 *    Rafael Antognolli <rafael.antognolli@intel.com>
 *
 */

#include <linux/device.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sched/signal.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/uio.h>

#include <drm/display/drm_dp_helper.h>
#include <drm/display/drm_dp_mst_helper.h>
#include <drm/drm_crtc.h>
#include <drm/drm_print.h>

#include "drm_dp_helper_internal.h"

struct drm_dp_aux_dev {
	unsigned index;
	struct drm_dp_aux *aux;
	struct device *dev;
	struct kref refcount;
	atomic_t usecount;
};

#define DRM_AUX_MINORS	256
#define AUX_MAX_OFFSET	(1 << 20)
static DEFINE_IDR(aux_idr);
static DEFINE_MUTEX(aux_idr_mutex);
static struct class *drm_dp_aux_dev_class;
static int drm_dev_major = -1;

static struct drm_dp_aux_dev *drm_dp_aux_dev_get_by_minor(unsigned index)
{
	struct drm_dp_aux_dev *aux_dev = NULL;

	mutex_lock(&aux_idr_mutex);
	aux_dev = idr_find(&aux_idr, index);
	if (aux_dev && !kref_get_unless_zero(&aux_dev->refcount))
		aux_dev = NULL;
	mutex_unlock(&aux_idr_mutex);

	return aux_dev;
}

static struct drm_dp_aux_dev *alloc_drm_dp_aux_dev(struct drm_dp_aux *aux)
{
	struct drm_dp_aux_dev *aux_dev;
	int index;

	aux_dev = kzalloc(sizeof(*aux_dev), GFP_KERNEL);
	if (!aux_dev)
		return ERR_PTR(-ENOMEM);
	aux_dev->aux = aux;
	atomic_set(&aux_dev->usecount, 1);
	kref_init(&aux_dev->refcount);

	mutex_lock(&aux_idr_mutex);
	index = idr_alloc(&aux_idr, aux_dev, 0, DRM_AUX_MINORS, GFP_KERNEL);
	mutex_unlock(&aux_idr_mutex);
	if (index < 0) {
		kfree(aux_dev);
		return ERR_PTR(index);
	}
	aux_dev->index = index;

	return aux_dev;
}

static void release_drm_dp_aux_dev(struct kref *ref)
{
	struct drm_dp_aux_dev *aux_dev =
		container_of(ref, struct drm_dp_aux_dev, refcount);

	kfree(aux_dev);
}

static ssize_t name_show(struct device *dev,
			 struct device_attribute *attr, char *buf)
{
	ssize_t res;
	struct drm_dp_aux_dev *aux_dev =
		drm_dp_aux_dev_get_by_minor(MINOR(dev->devt));

	if (!aux_dev)
		return -ENODEV;

	res = sprintf(buf, "%s\n", aux_dev->aux->name);
	kref_put(&aux_dev->refcount, release_drm_dp_aux_dev);

	return res;
}
static DEVICE_ATTR_RO(name);

static struct attribute *drm_dp_aux_attrs[] = {
	&dev_attr_name.attr,
	NULL,
};
ATTRIBUTE_GROUPS(drm_dp_aux);

static int auxdev_open(struct inode *inode, struct file *file)
{
	unsigned int minor = iminor(inode);
	struct drm_dp_aux_dev *aux_dev;

	aux_dev = drm_dp_aux_dev_get_by_minor(minor);
	if (!aux_dev)
		return -ENODEV;

	file->private_data = aux_dev;
	return 0;
}

static loff_t auxdev_llseek(struct file *file, loff_t offset, int whence)
{
	return fixed_size_llseek(file, offset, whence, AUX_MAX_OFFSET);
}

static ssize_t auxdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
	struct drm_dp_aux_dev *aux_dev = iocb->ki_filp->private_data;
	loff_t pos = iocb->ki_pos;
	ssize_t res = 0;

	if (!atomic_inc_not_zero(&aux_dev->usecount))
		return -ENODEV;

	iov_iter_truncate(to, AUX_MAX_OFFSET - pos);

	while (iov_iter_count(to)) {
		uint8_t buf[DP_AUX_MAX_PAYLOAD_BYTES];
		ssize_t todo = min(iov_iter_count(to), sizeof(buf));

		if (signal_pending(current)) {
			res = -ERESTARTSYS;
			break;
		}

		res = drm_dp_dpcd_read(aux_dev->aux, pos, buf, todo);

		if (res <= 0)
			break;

		if (copy_to_iter(buf, res, to) != res) {
			res = -EFAULT;
			break;
		}

		pos += res;
	}

	if (pos != iocb->ki_pos)
		res = pos - iocb->ki_pos;
	iocb->ki_pos = pos;

	if (atomic_dec_and_test(&aux_dev->usecount))
		wake_up_var(&aux_dev->usecount);

	return res;
}

static ssize_t auxdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
	struct drm_dp_aux_dev *aux_dev = iocb->ki_filp->private_data;
	loff_t pos = iocb->ki_pos;
	ssize_t res = 0;

	if (!atomic_inc_not_zero(&aux_dev->usecount))
		return -ENODEV;

	iov_iter_truncate(from, AUX_MAX_OFFSET - pos);

	while (iov_iter_count(from)) {
		uint8_t buf[DP_AUX_MAX_PAYLOAD_BYTES];
		ssize_t todo = min(iov_iter_count(from), sizeof(buf));

		if (signal_pending(current)) {
			res = -ERESTARTSYS;
			break;
		}

		if (!copy_from_iter_full(buf, todo, from)) {
			res = -EFAULT;
			break;
		}

		res = drm_dp_dpcd_write(aux_dev->aux, pos, buf, todo);

		if (res <= 0)
			break;

		pos += res;
	}

	if (pos != iocb->ki_pos)
		res = pos - iocb->ki_pos;
	iocb->ki_pos = pos;

	if (atomic_dec_and_test(&aux_dev->usecount))
		wake_up_var(&aux_dev->usecount);

	return res;
}

static int auxdev_release(struct inode *inode, struct file *file)
{
	struct drm_dp_aux_dev *aux_dev = file->private_data;

	kref_put(&aux_dev->refcount, release_drm_dp_aux_dev);
	return 0;
}

static const struct file_operations auxdev_fops = {
	.owner		= THIS_MODULE,
	.llseek		= auxdev_llseek,
	.read_iter	= auxdev_read_iter,
	.write_iter	= auxdev_write_iter,
	.open		= auxdev_open,
	.release	= auxdev_release,
};

#define to_auxdev(d) container_of(d, struct drm_dp_aux_dev, aux)

static struct drm_dp_aux_dev *drm_dp_aux_dev_get_by_aux(struct drm_dp_aux *aux)
{
	struct drm_dp_aux_dev *iter, *aux_dev = NULL;
	int id;

	/* don't increase kref count here because this function should only be
	 * used by drm_dp_aux_unregister_devnode. Thus, it will always have at
	 * least one reference - the one that drm_dp_aux_register_devnode
	 * created
	 */
	mutex_lock(&aux_idr_mutex);
	idr_for_each_entry(&aux_idr, iter, id) {
		if (iter->aux == aux) {
			aux_dev = iter;
			break;
		}
	}
	mutex_unlock(&aux_idr_mutex);
	return aux_dev;
}

void drm_dp_aux_unregister_devnode(struct drm_dp_aux *aux)
{
	struct drm_dp_aux_dev *aux_dev;
	unsigned int minor;

	aux_dev = drm_dp_aux_dev_get_by_aux(aux);
	if (!aux_dev) /* attach must have failed */
		return;

	/*
	 * As some AUX adapters may exist as platform devices which outlive their respective DRM
	 * devices, we clear drm_dev to ensure that we never accidentally reference a stale pointer
	 */
	aux->drm_dev = NULL;

	mutex_lock(&aux_idr_mutex);
	idr_remove(&aux_idr, aux_dev->index);
	mutex_unlock(&aux_idr_mutex);

	atomic_dec(&aux_dev->usecount);
	wait_var_event(&aux_dev->usecount, !atomic_read(&aux_dev->usecount));

	minor = aux_dev->index;
	if (aux_dev->dev)
		device_destroy(drm_dp_aux_dev_class,
			       MKDEV(drm_dev_major, minor));

	DRM_DEBUG("drm_dp_aux_dev: aux [%s] unregistering\n", aux->name);
	kref_put(&aux_dev->refcount, release_drm_dp_aux_dev);
}

int drm_dp_aux_register_devnode(struct drm_dp_aux *aux)
{
	struct drm_dp_aux_dev *aux_dev;
	int res;

	aux_dev = alloc_drm_dp_aux_dev(aux);
	if (IS_ERR(aux_dev))
		return PTR_ERR(aux_dev);

	aux_dev->dev = device_create(drm_dp_aux_dev_class, aux->dev,
				     MKDEV(drm_dev_major, aux_dev->index), NULL,
				     "drm_dp_aux%d", aux_dev->index);
	if (IS_ERR(aux_dev->dev)) {
		res = PTR_ERR(aux_dev->dev);
		aux_dev->dev = NULL;
		goto error;
	}

	DRM_DEBUG("drm_dp_aux_dev: aux [%s] registered as minor %d\n",
		  aux->name, aux_dev->index);
	return 0;
error:
	drm_dp_aux_unregister_devnode(aux);
	return res;
}

int drm_dp_aux_dev_init(void)
{
	int res;

	drm_dp_aux_dev_class = class_create(THIS_MODULE, "drm_dp_aux_dev");
	if (IS_ERR(drm_dp_aux_dev_class)) {
		return PTR_ERR(drm_dp_aux_dev_class);
	}
	drm_dp_aux_dev_class->dev_groups = drm_dp_aux_groups;

	res = register_chrdev(0, "aux", &auxdev_fops);
	if (res < 0)
		goto out;
	drm_dev_major = res;

	return 0;
out:
	class_destroy(drm_dp_aux_dev_class);
	return res;
}

void drm_dp_aux_dev_exit(void)
{
	unregister_chrdev(drm_dev_major, "aux");
	class_destroy(drm_dp_aux_dev_class);
}