Contributors: 10
Author Tokens Token Proportion Commits Commit Proportion
Gerd Hoffmann 2993 85.20% 1 4.17%
Jason Gunthorpe 222 6.32% 8 33.33%
Yi L Liu 141 4.01% 3 12.50%
Christoph Hellwig 107 3.05% 6 25.00%
Max Gurtovoy 25 0.71% 1 4.17%
Alex Williamson 9 0.26% 1 4.17%
Chengguang Xu 8 0.23% 1 4.17%
Colin Ian King 5 0.14% 1 4.17%
Stefan Hajnoczi 2 0.06% 1 4.17%
Jann Horn 1 0.03% 1 4.17%
Total 3513 24 


// SPDX-License-Identifier: GPL-2.0
/*
 * Mediated virtual PCI display host device driver
 *
 * See mdpy-defs.h for device specs
 *
 *   (c) Gerd Hoffmann <kraxel@redhat.com>
 *
 * based on mtty driver which is:
 *   Copyright (c) 2016, NVIDIA CORPORATION. All rights reserved.
 *	 Author: Neo Jia <cjia@nvidia.com>
 *		 Kirti Wankhede <kwankhede@nvidia.com>
 *
 * 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.
 */
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/cdev.h>
#include <linux/vfio.h>
#include <linux/iommu.h>
#include <linux/sysfs.h>
#include <linux/mdev.h>
#include <linux/pci.h>
#include <drm/drm_fourcc.h>
#include "mdpy-defs.h"

#define MDPY_NAME		"mdpy"
#define MDPY_CLASS_NAME		"mdpy"

#define MDPY_CONFIG_SPACE_SIZE	0xff
#define MDPY_MEMORY_BAR_OFFSET	PAGE_SIZE
#define MDPY_DISPLAY_REGION	16

#define STORE_LE16(addr, val)	(*(u16 *)addr = val)
#define STORE_LE32(addr, val)	(*(u32 *)addr = val)


MODULE_LICENSE("GPL v2");

#define MDPY_TYPE_1 "vga"
#define MDPY_TYPE_2 "xga"
#define MDPY_TYPE_3 "hd"

static struct mdpy_type {
	struct mdev_type type;
	u32 format;
	u32 bytepp;
	u32 width;
	u32 height;
} mdpy_types[] = {
	{
		.type.sysfs_name 	= MDPY_TYPE_1,
		.type.pretty_name	= MDPY_CLASS_NAME "-" MDPY_TYPE_1,
		.format = DRM_FORMAT_XRGB8888,
		.bytepp = 4,
		.width	= 640,
		.height = 480,
	}, {
		.type.sysfs_name 	= MDPY_TYPE_2,
		.type.pretty_name	= MDPY_CLASS_NAME "-" MDPY_TYPE_2,
		.format = DRM_FORMAT_XRGB8888,
		.bytepp = 4,
		.width	= 1024,
		.height = 768,
	}, {
		.type.sysfs_name 	= MDPY_TYPE_3,
		.type.pretty_name	= MDPY_CLASS_NAME "-" MDPY_TYPE_3,
		.format = DRM_FORMAT_XRGB8888,
		.bytepp = 4,
		.width	= 1920,
		.height = 1080,
	},
};

static struct mdev_type *mdpy_mdev_types[] = {
	&mdpy_types[0].type,
	&mdpy_types[1].type,
	&mdpy_types[2].type,
};

static dev_t		mdpy_devt;
static struct class	*mdpy_class;
static struct cdev	mdpy_cdev;
static struct device	mdpy_dev;
static struct mdev_parent mdpy_parent;
static const struct vfio_device_ops mdpy_dev_ops;

/* State of each mdev device */
struct mdev_state {
	struct vfio_device vdev;
	u8 *vconfig;
	u32 bar_mask;
	struct mutex ops_lock;
	struct mdev_device *mdev;
	struct vfio_device_info dev_info;

	const struct mdpy_type *type;
	u32 memsize;
	void *memblk;
};

static void mdpy_create_config_space(struct mdev_state *mdev_state)
{
	STORE_LE16((u16 *) &mdev_state->vconfig[PCI_VENDOR_ID],
		   MDPY_PCI_VENDOR_ID);
	STORE_LE16((u16 *) &mdev_state->vconfig[PCI_DEVICE_ID],
		   MDPY_PCI_DEVICE_ID);
	STORE_LE16((u16 *) &mdev_state->vconfig[PCI_SUBSYSTEM_VENDOR_ID],
		   MDPY_PCI_SUBVENDOR_ID);
	STORE_LE16((u16 *) &mdev_state->vconfig[PCI_SUBSYSTEM_ID],
		   MDPY_PCI_SUBDEVICE_ID);

	STORE_LE16((u16 *) &mdev_state->vconfig[PCI_COMMAND],
		   PCI_COMMAND_IO | PCI_COMMAND_MEMORY);
	STORE_LE16((u16 *) &mdev_state->vconfig[PCI_STATUS],
		   PCI_STATUS_CAP_LIST);
	STORE_LE16((u16 *) &mdev_state->vconfig[PCI_CLASS_DEVICE],
		   PCI_CLASS_DISPLAY_OTHER);
	mdev_state->vconfig[PCI_CLASS_REVISION] =  0x01;

	STORE_LE32((u32 *) &mdev_state->vconfig[PCI_BASE_ADDRESS_0],
		   PCI_BASE_ADDRESS_SPACE_MEMORY |
		   PCI_BASE_ADDRESS_MEM_TYPE_32	 |
		   PCI_BASE_ADDRESS_MEM_PREFETCH);
	mdev_state->bar_mask = ~(mdev_state->memsize) + 1;

	/* vendor specific capability for the config registers */
	mdev_state->vconfig[PCI_CAPABILITY_LIST]       = MDPY_VENDORCAP_OFFSET;
	mdev_state->vconfig[MDPY_VENDORCAP_OFFSET + 0] = 0x09; /* vendor cap */
	mdev_state->vconfig[MDPY_VENDORCAP_OFFSET + 1] = 0x00; /* next ptr */
	mdev_state->vconfig[MDPY_VENDORCAP_OFFSET + 2] = MDPY_VENDORCAP_SIZE;
	STORE_LE32((u32 *) &mdev_state->vconfig[MDPY_FORMAT_OFFSET],
		   mdev_state->type->format);
	STORE_LE32((u32 *) &mdev_state->vconfig[MDPY_WIDTH_OFFSET],
		   mdev_state->type->width);
	STORE_LE32((u32 *) &mdev_state->vconfig[MDPY_HEIGHT_OFFSET],
		   mdev_state->type->height);
}

static void handle_pci_cfg_write(struct mdev_state *mdev_state, u16 offset,
				 char *buf, u32 count)
{
	struct device *dev = mdev_dev(mdev_state->mdev);
	u32 cfg_addr;

	switch (offset) {
	case PCI_BASE_ADDRESS_0:
		cfg_addr = *(u32 *)buf;

		if (cfg_addr == 0xffffffff) {
			cfg_addr = (cfg_addr & mdev_state->bar_mask);
		} else {
			cfg_addr &= PCI_BASE_ADDRESS_MEM_MASK;
			if (cfg_addr)
				dev_info(dev, "BAR0 @ 0x%x\n", cfg_addr);
		}

		cfg_addr |= (mdev_state->vconfig[offset] &
			     ~PCI_BASE_ADDRESS_MEM_MASK);
		STORE_LE32(&mdev_state->vconfig[offset], cfg_addr);
		break;
	}
}

static ssize_t mdev_access(struct mdev_state *mdev_state, char *buf,
			   size_t count, loff_t pos, bool is_write)
{
	int ret = 0;

	mutex_lock(&mdev_state->ops_lock);

	if (pos < MDPY_CONFIG_SPACE_SIZE) {
		if (is_write)
			handle_pci_cfg_write(mdev_state, pos, buf, count);
		else
			memcpy(buf, (mdev_state->vconfig + pos), count);

	} else if ((pos >= MDPY_MEMORY_BAR_OFFSET) &&
		   (pos + count <=
		    MDPY_MEMORY_BAR_OFFSET + mdev_state->memsize)) {
		pos -= MDPY_MEMORY_BAR_OFFSET;
		if (is_write)
			memcpy(mdev_state->memblk, buf, count);
		else
			memcpy(buf, mdev_state->memblk, count);

	} else {
		dev_info(mdev_state->vdev.dev,
			 "%s: %s @0x%llx (unhandled)\n", __func__,
			 is_write ? "WR" : "RD", pos);
		ret = -1;
		goto accessfailed;
	}

	ret = count;


accessfailed:
	mutex_unlock(&mdev_state->ops_lock);

	return ret;
}

static int mdpy_reset(struct mdev_state *mdev_state)
{
	u32 stride, i;

	/* initialize with gray gradient */
	stride = mdev_state->type->width * mdev_state->type->bytepp;
	for (i = 0; i < mdev_state->type->height; i++)
		memset(mdev_state->memblk + i * stride,
		       i * 255 / mdev_state->type->height,
		       stride);
	return 0;
}

static int mdpy_init_dev(struct vfio_device *vdev)
{
	struct mdev_state *mdev_state =
		container_of(vdev, struct mdev_state, vdev);
	struct mdev_device *mdev = to_mdev_device(vdev->dev);
	const struct mdpy_type *type =
		container_of(mdev->type, struct mdpy_type, type);
	u32 fbsize;
	int ret = -ENOMEM;

	mdev_state->vconfig = kzalloc(MDPY_CONFIG_SPACE_SIZE, GFP_KERNEL);
	if (!mdev_state->vconfig)
		return ret;

	fbsize = roundup_pow_of_two(type->width * type->height * type->bytepp);

	mdev_state->memblk = vmalloc_user(fbsize);
	if (!mdev_state->memblk)
		goto out_vconfig;

	mutex_init(&mdev_state->ops_lock);
	mdev_state->mdev = mdev;
	mdev_state->type = type;
	mdev_state->memsize = fbsize;
	mdpy_create_config_space(mdev_state);
	mdpy_reset(mdev_state);

	dev_info(vdev->dev, "%s: %s (%dx%d)\n", __func__, type->type.pretty_name,
		 type->width, type->height);
	return 0;

out_vconfig:
	kfree(mdev_state->vconfig);
	return ret;
}

static int mdpy_probe(struct mdev_device *mdev)
{
	struct mdev_state *mdev_state;
	int ret;

	mdev_state = vfio_alloc_device(mdev_state, vdev, &mdev->dev,
				       &mdpy_dev_ops);
	if (IS_ERR(mdev_state))
		return PTR_ERR(mdev_state);

	ret = vfio_register_emulated_iommu_dev(&mdev_state->vdev);
	if (ret)
		goto err_put_vdev;
	dev_set_drvdata(&mdev->dev, mdev_state);
	return 0;

err_put_vdev:
	vfio_put_device(&mdev_state->vdev);
	return ret;
}

static void mdpy_release_dev(struct vfio_device *vdev)
{
	struct mdev_state *mdev_state =
		container_of(vdev, struct mdev_state, vdev);

	vfree(mdev_state->memblk);
	kfree(mdev_state->vconfig);
}

static void mdpy_remove(struct mdev_device *mdev)
{
	struct mdev_state *mdev_state = dev_get_drvdata(&mdev->dev);

	dev_info(&mdev->dev, "%s\n", __func__);

	vfio_unregister_group_dev(&mdev_state->vdev);
	vfio_put_device(&mdev_state->vdev);
}

static ssize_t mdpy_read(struct vfio_device *vdev, char __user *buf,
			 size_t count, loff_t *ppos)
{
	struct mdev_state *mdev_state =
		container_of(vdev, struct mdev_state, vdev);
	unsigned int done = 0;
	int ret;

	while (count) {
		size_t filled;

		if (count >= 4 && !(*ppos % 4)) {
			u32 val;

			ret = mdev_access(mdev_state, (char *)&val, sizeof(val),
					  *ppos, false);
			if (ret <= 0)
				goto read_err;

			if (copy_to_user(buf, &val, sizeof(val)))
				goto read_err;

			filled = 4;
		} else if (count >= 2 && !(*ppos % 2)) {
			u16 val;

			ret = mdev_access(mdev_state, (char *)&val, sizeof(val),
					  *ppos, false);
			if (ret <= 0)
				goto read_err;

			if (copy_to_user(buf, &val, sizeof(val)))
				goto read_err;

			filled = 2;
		} else {
			u8 val;

			ret = mdev_access(mdev_state, (char *)&val, sizeof(val),
					  *ppos, false);
			if (ret <= 0)
				goto read_err;

			if (copy_to_user(buf, &val, sizeof(val)))
				goto read_err;

			filled = 1;
		}

		count -= filled;
		done += filled;
		*ppos += filled;
		buf += filled;
	}

	return done;

read_err:
	return -EFAULT;
}

static ssize_t mdpy_write(struct vfio_device *vdev, const char __user *buf,
			  size_t count, loff_t *ppos)
{
	struct mdev_state *mdev_state =
		container_of(vdev, struct mdev_state, vdev);
	unsigned int done = 0;
	int ret;

	while (count) {
		size_t filled;

		if (count >= 4 && !(*ppos % 4)) {
			u32 val;

			if (copy_from_user(&val, buf, sizeof(val)))
				goto write_err;

			ret = mdev_access(mdev_state, (char *)&val, sizeof(val),
					  *ppos, true);
			if (ret <= 0)
				goto write_err;

			filled = 4;
		} else if (count >= 2 && !(*ppos % 2)) {
			u16 val;

			if (copy_from_user(&val, buf, sizeof(val)))
				goto write_err;

			ret = mdev_access(mdev_state, (char *)&val, sizeof(val),
					  *ppos, true);
			if (ret <= 0)
				goto write_err;

			filled = 2;
		} else {
			u8 val;

			if (copy_from_user(&val, buf, sizeof(val)))
				goto write_err;

			ret = mdev_access(mdev_state, (char *)&val, sizeof(val),
					  *ppos, true);
			if (ret <= 0)
				goto write_err;

			filled = 1;
		}
		count -= filled;
		done += filled;
		*ppos += filled;
		buf += filled;
	}

	return done;
write_err:
	return -EFAULT;
}

static int mdpy_mmap(struct vfio_device *vdev, struct vm_area_struct *vma)
{
	struct mdev_state *mdev_state =
		container_of(vdev, struct mdev_state, vdev);

	if (vma->vm_pgoff != MDPY_MEMORY_BAR_OFFSET >> PAGE_SHIFT)
		return -EINVAL;
	if (vma->vm_end < vma->vm_start)
		return -EINVAL;
	if (vma->vm_end - vma->vm_start > mdev_state->memsize)
		return -EINVAL;
	if ((vma->vm_flags & VM_SHARED) == 0)
		return -EINVAL;

	return remap_vmalloc_range(vma, mdev_state->memblk, 0);
}

static int mdpy_get_region_info(struct mdev_state *mdev_state,
				struct vfio_region_info *region_info,
				u16 *cap_type_id, void **cap_type)
{
	if (region_info->index >= VFIO_PCI_NUM_REGIONS &&
	    region_info->index != MDPY_DISPLAY_REGION)
		return -EINVAL;

	switch (region_info->index) {
	case VFIO_PCI_CONFIG_REGION_INDEX:
		region_info->offset = 0;
		region_info->size   = MDPY_CONFIG_SPACE_SIZE;
		region_info->flags  = (VFIO_REGION_INFO_FLAG_READ |
				       VFIO_REGION_INFO_FLAG_WRITE);
		break;
	case VFIO_PCI_BAR0_REGION_INDEX:
	case MDPY_DISPLAY_REGION:
		region_info->offset = MDPY_MEMORY_BAR_OFFSET;
		region_info->size   = mdev_state->memsize;
		region_info->flags  = (VFIO_REGION_INFO_FLAG_READ  |
				       VFIO_REGION_INFO_FLAG_WRITE |
				       VFIO_REGION_INFO_FLAG_MMAP);
		break;
	default:
		region_info->size   = 0;
		region_info->offset = 0;
		region_info->flags  = 0;
	}

	return 0;
}

static int mdpy_get_irq_info(struct vfio_irq_info *irq_info)
{
	irq_info->count = 0;
	return 0;
}

static int mdpy_get_device_info(struct vfio_device_info *dev_info)
{
	dev_info->flags = VFIO_DEVICE_FLAGS_PCI;
	dev_info->num_regions = VFIO_PCI_NUM_REGIONS;
	dev_info->num_irqs = VFIO_PCI_NUM_IRQS;
	return 0;
}

static int mdpy_query_gfx_plane(struct mdev_state *mdev_state,
				struct vfio_device_gfx_plane_info *plane)
{
	if (plane->flags & VFIO_GFX_PLANE_TYPE_PROBE) {
		if (plane->flags == (VFIO_GFX_PLANE_TYPE_PROBE |
				     VFIO_GFX_PLANE_TYPE_REGION))
			return 0;
		return -EINVAL;
	}

	if (plane->flags != VFIO_GFX_PLANE_TYPE_REGION)
		return -EINVAL;

	plane->drm_format     = mdev_state->type->format;
	plane->width	      = mdev_state->type->width;
	plane->height	      = mdev_state->type->height;
	plane->stride	      = (mdev_state->type->width *
				 mdev_state->type->bytepp);
	plane->size	      = mdev_state->memsize;
	plane->region_index   = MDPY_DISPLAY_REGION;

	/* unused */
	plane->drm_format_mod = 0;
	plane->x_pos	      = 0;
	plane->y_pos	      = 0;
	plane->x_hot	      = 0;
	plane->y_hot	      = 0;

	return 0;
}

static long mdpy_ioctl(struct vfio_device *vdev, unsigned int cmd,
		       unsigned long arg)
{
	int ret = 0;
	unsigned long minsz;
	struct mdev_state *mdev_state =
		container_of(vdev, struct mdev_state, vdev);

	switch (cmd) {
	case VFIO_DEVICE_GET_INFO:
	{
		struct vfio_device_info info;

		minsz = offsetofend(struct vfio_device_info, num_irqs);

		if (copy_from_user(&info, (void __user *)arg, minsz))
			return -EFAULT;

		if (info.argsz < minsz)
			return -EINVAL;

		ret = mdpy_get_device_info(&info);
		if (ret)
			return ret;

		memcpy(&mdev_state->dev_info, &info, sizeof(info));

		if (copy_to_user((void __user *)arg, &info, minsz))
			return -EFAULT;

		return 0;
	}
	case VFIO_DEVICE_GET_REGION_INFO:
	{
		struct vfio_region_info info;
		u16 cap_type_id = 0;
		void *cap_type = NULL;

		minsz = offsetofend(struct vfio_region_info, offset);

		if (copy_from_user(&info, (void __user *)arg, minsz))
			return -EFAULT;

		if (info.argsz < minsz)
			return -EINVAL;

		ret = mdpy_get_region_info(mdev_state, &info, &cap_type_id,
					   &cap_type);
		if (ret)
			return ret;

		if (copy_to_user((void __user *)arg, &info, minsz))
			return -EFAULT;

		return 0;
	}

	case VFIO_DEVICE_GET_IRQ_INFO:
	{
		struct vfio_irq_info info;

		minsz = offsetofend(struct vfio_irq_info, count);

		if (copy_from_user(&info, (void __user *)arg, minsz))
			return -EFAULT;

		if ((info.argsz < minsz) ||
		    (info.index >= mdev_state->dev_info.num_irqs))
			return -EINVAL;

		ret = mdpy_get_irq_info(&info);
		if (ret)
			return ret;

		if (copy_to_user((void __user *)arg, &info, minsz))
			return -EFAULT;

		return 0;
	}

	case VFIO_DEVICE_QUERY_GFX_PLANE:
	{
		struct vfio_device_gfx_plane_info plane = {};

		minsz = offsetofend(struct vfio_device_gfx_plane_info,
				    region_index);

		if (copy_from_user(&plane, (void __user *)arg, minsz))
			return -EFAULT;

		if (plane.argsz < minsz)
			return -EINVAL;

		ret = mdpy_query_gfx_plane(mdev_state, &plane);
		if (ret)
			return ret;

		if (copy_to_user((void __user *)arg, &plane, minsz))
			return -EFAULT;

		return 0;
	}

	case VFIO_DEVICE_SET_IRQS:
		return -EINVAL;

	case VFIO_DEVICE_RESET:
		return mdpy_reset(mdev_state);
	}
	return -ENOTTY;
}

static ssize_t
resolution_show(struct device *dev, struct device_attribute *attr,
		char *buf)
{
	struct mdev_state *mdev_state = dev_get_drvdata(dev);

	return sprintf(buf, "%dx%d\n",
		       mdev_state->type->width,
		       mdev_state->type->height);
}
static DEVICE_ATTR_RO(resolution);

static struct attribute *mdev_dev_attrs[] = {
	&dev_attr_resolution.attr,
	NULL,
};

static const struct attribute_group mdev_dev_group = {
	.name  = "vendor",
	.attrs = mdev_dev_attrs,
};

static const struct attribute_group *mdev_dev_groups[] = {
	&mdev_dev_group,
	NULL,
};

static ssize_t mdpy_show_description(struct mdev_type *mtype, char *buf)
{
	struct mdpy_type *type = container_of(mtype, struct mdpy_type, type);

	return sprintf(buf, "virtual display, %dx%d framebuffer\n",
		       type->width, type->height);
}

static const struct vfio_device_ops mdpy_dev_ops = {
	.init = mdpy_init_dev,
	.release = mdpy_release_dev,
	.read = mdpy_read,
	.write = mdpy_write,
	.ioctl = mdpy_ioctl,
	.mmap = mdpy_mmap,
	.bind_iommufd	= vfio_iommufd_emulated_bind,
	.unbind_iommufd	= vfio_iommufd_emulated_unbind,
	.attach_ioas	= vfio_iommufd_emulated_attach_ioas,
	.detach_ioas	= vfio_iommufd_emulated_detach_ioas,
};

static struct mdev_driver mdpy_driver = {
	.device_api = VFIO_DEVICE_API_PCI_STRING,
	.max_instances = 4,
	.driver = {
		.name = "mdpy",
		.owner = THIS_MODULE,
		.mod_name = KBUILD_MODNAME,
		.dev_groups = mdev_dev_groups,
	},
	.probe = mdpy_probe,
	.remove	= mdpy_remove,
	.show_description = mdpy_show_description,
};

static const struct file_operations vd_fops = {
	.owner		= THIS_MODULE,
};

static void mdpy_device_release(struct device *dev)
{
	/* nothing */
}

static int __init mdpy_dev_init(void)
{
	int ret = 0;

	ret = alloc_chrdev_region(&mdpy_devt, 0, MINORMASK + 1, MDPY_NAME);
	if (ret < 0) {
		pr_err("Error: failed to register mdpy_dev, err: %d\n", ret);
		return ret;
	}
	cdev_init(&mdpy_cdev, &vd_fops);
	cdev_add(&mdpy_cdev, mdpy_devt, MINORMASK + 1);
	pr_info("%s: major %d\n", __func__, MAJOR(mdpy_devt));

	ret = mdev_register_driver(&mdpy_driver);
	if (ret)
		goto err_cdev;

	mdpy_class = class_create(MDPY_CLASS_NAME);
	if (IS_ERR(mdpy_class)) {
		pr_err("Error: failed to register mdpy_dev class\n");
		ret = PTR_ERR(mdpy_class);
		goto err_driver;
	}
	mdpy_dev.class = mdpy_class;
	mdpy_dev.release = mdpy_device_release;
	dev_set_name(&mdpy_dev, "%s", MDPY_NAME);

	ret = device_register(&mdpy_dev);
	if (ret)
		goto err_put;

	ret = mdev_register_parent(&mdpy_parent, &mdpy_dev, &mdpy_driver,
				   mdpy_mdev_types,
				   ARRAY_SIZE(mdpy_mdev_types));
	if (ret)
		goto err_device;

	return 0;

err_device:
	device_del(&mdpy_dev);
err_put:
	put_device(&mdpy_dev);
	class_destroy(mdpy_class);
err_driver:
	mdev_unregister_driver(&mdpy_driver);
err_cdev:
	cdev_del(&mdpy_cdev);
	unregister_chrdev_region(mdpy_devt, MINORMASK + 1);
	return ret;
}

static void __exit mdpy_dev_exit(void)
{
	mdpy_dev.bus = NULL;
	mdev_unregister_parent(&mdpy_parent);

	device_unregister(&mdpy_dev);
	mdev_unregister_driver(&mdpy_driver);
	cdev_del(&mdpy_cdev);
	unregister_chrdev_region(mdpy_devt, MINORMASK + 1);
	class_destroy(mdpy_class);
	mdpy_class = NULL;
}

module_param_named(count, mdpy_driver.max_instances, int, 0444);
MODULE_PARM_DESC(count, "number of " MDPY_NAME " devices");

module_init(mdpy_dev_init)
module_exit(mdpy_dev_exit)