Re: [PATCH v4 2/2] drm/dp: Add a drm_aux-dev module for reading/writing dpcd registers.

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Sep 28, 2015 at 04:45:36PM -0700, Rafael Antognolli wrote:
> This module is heavily based on i2c-dev. Once loaded, it provides one
> dev node per DP AUX channel, named drm_dp_auxN, where N is an integer.
> 
> It's possible to know which connector owns this aux channel by looking
> at the respective sysfs /sys/class/drm_aux_dev/drm_dp_auxN/connector, if
> the connector device pointer was correctly set in the aux helper struct.
> 
> Two main operations are provided on the registers read and write. The
> address of the register to be read or written is given using lseek. The
> seek position is updated upon read or write.
> 
> Signed-off-by: Rafael Antognolli <rafael.antognolli@intel.com>
> ---
>  drivers/gpu/drm/Kconfig          |   8 +
>  drivers/gpu/drm/Makefile         |   1 +
>  drivers/gpu/drm/drm_dp_aux_dev.c | 357 +++++++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/drm_dp_helper.c  |   5 +
>  include/drm/drm_dp_aux_dev.h     |  50 ++++++
>  5 files changed, 421 insertions(+)
>  create mode 100644 drivers/gpu/drm/drm_dp_aux_dev.c
>  create mode 100644 include/drm/drm_dp_aux_dev.h
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 1a0a8df..64fa0f4 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -25,6 +25,14 @@ config DRM_MIPI_DSI
>  	bool
>  	depends on DRM
>  
> +config DRM_DP_AUX_CHARDEV
> +	bool "DRM DP AUX Interface"
> +	depends on DRM
> +	help
> +	  Choose this option to enable a /dev/drm_dp_auxN node that allows to
> +	  read and write values to arbitrary DPCD registers on the DP aux
> +	  channel.
> +
>  config DRM_KMS_HELPER
>  	tristate
>  	depends on DRM
> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> index 45e7719..e5ae7f0 100644
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -25,6 +25,7 @@ drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_probe_helper.o \
>  drm_kms_helper-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
>  drm_kms_helper-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fb_helper.o
>  drm_kms_helper-$(CONFIG_DRM_KMS_CMA_HELPER) += drm_fb_cma_helper.o
> +drm_kms_helper-$(CONFIG_DRM_DP_AUX_CHARDEV) += drm_dp_aux_dev.o
>  
>  obj-$(CONFIG_DRM_KMS_HELPER) += drm_kms_helper.o
>  
> diff --git a/drivers/gpu/drm/drm_dp_aux_dev.c b/drivers/gpu/drm/drm_dp_aux_dev.c
> new file mode 100644
> index 0000000..e337081
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_dp_aux_dev.c
> @@ -0,0 +1,357 @@
> +/*
> + * 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/slab.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <asm/uaccess.h>
> +#include <drm/drm_dp_helper.h>
> +#include <drm/drm_crtc.h>
> +
> +struct drm_dp_aux_dev {
> +	struct list_head list;
> +	unsigned index;
> +	struct drm_dp_aux *aux;
> +	struct device *dev;
> +};
> +
> +#define DRM_AUX_MINORS	256
> +static int aux_max_offset = 1 << 20;

People seem to prefer defines for such things.

> +static int drm_dp_aux_dev_count = 0;
> +static LIST_HEAD(drm_dp_aux_dev_list);
> +static DEFINE_SPINLOCK(drm_dp_aux_dev_list_lock);
> +
> +static struct drm_dp_aux_dev *drm_dp_aux_dev_get_by_minor(unsigned index)
> +{
> +	struct drm_dp_aux_dev *aux_dev;
> +
> +	spin_lock(&drm_dp_aux_dev_list_lock);
> +	list_for_each_entry(aux_dev, &drm_dp_aux_dev_list, list) {
> +		if (aux_dev->index == index)
> +			goto found;
> +	}
> +
> +	aux_dev = NULL;
> +found:
> +	spin_unlock(&drm_dp_aux_dev_list_lock);
> +	return aux_dev;
> +}
> +
> +static struct drm_dp_aux_dev *drm_dp_aux_dev_get_by_aux(struct drm_dp_aux *aux)
> +{
> +	struct drm_dp_aux_dev *aux_dev;
> +
> +	spin_lock(&drm_dp_aux_dev_list_lock);
> +	list_for_each_entry(aux_dev, &drm_dp_aux_dev_list, list) {
> +		if (aux_dev->aux == aux)
> +			goto found;
> +	}
> +
> +	aux_dev = NULL;
> +found:
> +	spin_unlock(&drm_dp_aux_dev_list_lock);
> +	return aux_dev;
> +}
> +
> +static struct drm_dp_aux_dev *get_free_drm_dp_aux_dev(struct drm_dp_aux *aux)
> +{
> +	struct drm_dp_aux_dev *aux_dev;
> +	int index;
> +
> +	spin_lock(&drm_dp_aux_dev_list_lock);
> +	index = drm_dp_aux_dev_count;
> +	spin_unlock(&drm_dp_aux_dev_list_lock);
> +	if (index >= DRM_AUX_MINORS) {
> +		printk(KERN_ERR "drm_dp_aux_dev: Out of device minors (%d)\n",
> +		       index);
> +		return ERR_PTR(-ENODEV);
> +	}
> +
> +	aux_dev = kzalloc(sizeof(*aux_dev), GFP_KERNEL);
> +	if (!aux_dev)
> +		return ERR_PTR(-ENOMEM);
> +	aux_dev->aux = aux;
> +	aux_dev->index = index;
> +
> +	spin_lock(&drm_dp_aux_dev_list_lock);
> +	drm_dp_aux_dev_count++;

That's racy. Someone else could have snuck in and pushed
drm_dp_aux_dev_count over the limit already.

Maybe we want to use an idr or something to allocate the
index?

> +	list_add_tail(&aux_dev->list, &drm_dp_aux_dev_list);
> +	spin_unlock(&drm_dp_aux_dev_list_lock);
> +	return aux_dev;
> +}
> +
> +static void return_drm_dp_aux_dev(struct drm_dp_aux_dev *aux_dev)
> +{
> +	spin_lock(&drm_dp_aux_dev_list_lock);
> +	list_del(&aux_dev->list);
> +	spin_unlock(&drm_dp_aux_dev_list_lock);
> +	kfree(aux_dev);
> +}

I'm not a fan of the get_free & return names. Maybe just alloc/free?

> +
> +static ssize_t name_show(struct device *dev,
> +			 struct device_attribute *attr, char *buf)
> +{
> +	struct drm_dp_aux_dev *aux_dev =
> +		drm_dp_aux_dev_get_by_minor(MINOR(dev->devt));
> +
> +	if (!aux_dev)
> +		return -ENODEV;
> +	return sprintf(buf, "%s\n", aux_dev->aux->name);
> +}
> +static DEVICE_ATTR_RO(name);
> +
> +static ssize_t connector_show(struct device *dev,
> +			      struct device_attribute *attr, char *buf)
> +{
> +	struct drm_dp_aux_dev *aux_dev =
> +		drm_dp_aux_dev_get_by_minor(MINOR(dev->devt));
> +	struct drm_dp_aux *aux;
> +	struct device *conn_dev;
> +	struct drm_connector *connector = NULL;
> +
> +	if (!aux_dev)
> +		return -ENODEV;
> +	aux = aux_dev->aux;
> +	conn_dev = aux->connector;
> +	if (!conn_dev)
> +		return sprintf(buf, "unknown\n");
> +
> +	connector = dev_get_drvdata(aux->connector);
> +
> +	return sprintf(buf, "%s\n", connector->name);
> +}
> +static DEVICE_ATTR_RO(connector);
> +
> +static struct attribute *drm_dp_aux_attrs[] = {
> +	&dev_attr_name.attr,
> +	&dev_attr_connector.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(struct file *file, char __user *buf, size_t count,
> +			   loff_t *offset)
> +{
> +	ssize_t bytes_pending, num_bytes_processed = 0;
> +	struct drm_dp_aux_dev *aux_dev = file->private_data;
> +
> +	bytes_pending = aux_max_offset - *offset;
> +	bytes_pending = count < bytes_pending ? count : bytes_pending;

I would write it as
bytes_pending = min(count, aux_max_offset - *offset);

> +	if (bytes_pending < 0)
> +		return -EFAULT;

Can this actually happen somehow?

> +
> +	if (!access_ok(VERIFY_WRITE, buf, bytes_pending))
> +		return -EFAULT;
> +
> +	while (bytes_pending > 0) {
> +		uint8_t localbuf[DP_AUX_MAX_PAYLOAD_BYTES];
> +		ssize_t todo = sizeof(localbuf);
> +		ssize_t res;
> +		todo = bytes_pending < todo ? bytes_pending : todo;

Would write it as
todo = min(bytes_pending, sizeof(localbuf));

> +
> +		res = drm_dp_dpcd_read(aux_dev->aux, *offset, localbuf, todo);
> +		if (res <= 0) {
> +			return num_bytes_processed ? num_bytes_processed : res;
> +		}

Could drop the extra {}

> +		if (__copy_to_user(buf + num_bytes_processed, localbuf, res)) {
> +			return num_bytes_processed ?
> +				num_bytes_processed : -EFAULT;
> +		}

ditto

> +		bytes_pending -= res;
> +		*offset += res;
> +		num_bytes_processed += res;
> +	}
> +
> +	return num_bytes_processed;
> +}
> +
> +static ssize_t auxdev_write(struct file *file, const char __user *buf,
> +			    size_t count, loff_t *offset)
> +{
> +	ssize_t bytes_pending, num_bytes_processed = 0;
> +	struct drm_dp_aux_dev *aux_dev = file->private_data;
> +
> +	bytes_pending = aux_max_offset - *offset;
> +	bytes_pending = count < bytes_pending ? count : bytes_pending;
> +	if (bytes_pending < 0)
> +		return -EFAULT;
> +
> +	if (!access_ok(VERIFY_READ, buf, bytes_pending))
> +		return -EFAULT;
> +
> +	while (bytes_pending > 0) {
> +		uint8_t localbuf[DP_AUX_MAX_PAYLOAD_BYTES];
> +		ssize_t todo = sizeof(localbuf);
> +		ssize_t res;
> +		todo = bytes_pending < todo ? bytes_pending : todo;
> +		if (__copy_from_user(localbuf,
> +				     buf + num_bytes_processed, todo)) {
> +			return num_bytes_processed ?
> +				num_bytes_processed : -EFAULT;
> +		}
> +
> +		res = drm_dp_dpcd_write(aux_dev->aux, *offset, localbuf, todo);
> +		if (res <= 0) {
> +			return num_bytes_processed ? num_bytes_processed : res;
> +		}

same comments for write as for read.

> +		bytes_pending -= res;
> +		*offset += res;
> +		num_bytes_processed += res;
> +	}
> +
> +	return num_bytes_processed;
> +}
> +
> +static const struct file_operations auxdev_fops = {
> +	.owner		= THIS_MODULE,
> +	.llseek		= auxdev_llseek,
> +	.read		= auxdev_read,
> +	.write		= auxdev_write,
> +	.open		= auxdev_open,
> +};
> +
> +static struct class *drm_dp_aux_dev_class;
> +static int drm_dev_major = -1;
> +
> +#define to_auxdev(d) container_of(d, struct drm_dp_aux_dev, aux)
> +
> +/**
> + * drm_dp_aux_register_devnode() - register a devnode for this aux channel
> + * @aux: DisplayPort AUX channel
> + *
> + * Returns 0 on success or a negative error code on failure.
> + */
> +int drm_dp_aux_register_devnode(struct drm_dp_aux *aux)
> +{
> +	struct drm_dp_aux_dev *aux_dev;
> +	int res;
> +
> +	aux_dev = get_free_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);
> +		goto error;
> +	}
> +
> +	pr_debug("drm_dp_aux_dev: aux [%s] registered as minor %d\n",
> +		 aux->name, aux_dev->index);
> +	return 0;
> +error:
> +	return_drm_dp_aux_dev(aux_dev);
> +	return res;
> +
> +}
> +
> +/**
> + * drm_dp_aux_unregister_devnode() - unregister a devnode for this aux channel
> + * @aux: DisplayPort AUX channel
> + *
> + * Returns 0 on success or a negative error code on failure.
> + */
> +int drm_dp_aux_unregister_devnode(struct drm_dp_aux *aux)
> +{
> +	int minor;
> +	struct drm_dp_aux_dev *aux_dev;
> +
> +	aux_dev = drm_dp_aux_dev_get_by_aux(aux);
> +	if (!aux_dev) /* attach must have failed */
> +		return 0;
> +
> +	minor = aux_dev->index;
> +	return_drm_dp_aux_dev(aux_dev);
> +	device_destroy(drm_dp_aux_dev_class, MKDEV(drm_dev_major, minor));

device_destroy before you free the auxdev seem safer.

What happens if someone has the device still open? Do we need to kref the
aux_dev and add some kind of dead flag or something?

> +
> +	pr_debug("drm_dp_aux_dev: aux [%s] unregistered\n", aux->name);
> +	return 0;
> +}
> +
> +static int __init drm_dp_aux_dev_init(void)
> +{
> +	int res;
> +
> +	printk(KERN_INFO "drm dp aux /dev entries driver\n");

I don't see much point in this printk.

> +
> +	res = register_chrdev(0, "aux", &auxdev_fops);
> +	if (res < 0)
> +		goto out;
> +	drm_dev_major = res;
> +
> +	drm_dp_aux_dev_class = class_create(THIS_MODULE, "drm_dp_aux_dev");
> +	if (IS_ERR(drm_dp_aux_dev_class)) {
> +		res = PTR_ERR(drm_dp_aux_dev_class);
> +		goto out_unreg_chrdev;
> +	}
> +	drm_dp_aux_dev_class->dev_groups = drm_dp_aux_groups;
> +
> +	return 0;
> +
> +out_unreg_chrdev:
> +	unregister_chrdev(drm_dev_major, "aux");
> +out:
> +	printk(KERN_ERR "%s: Driver Initialisation failed\n", __FILE__);
> +	return res;
> +}
> +
> +static void __exit drm_dp_aux_dev_exit(void)
> +{
> +	printk(KERN_INFO "drm dp aux /dev entries driver - unloading\n");

ditto

> +	class_destroy(drm_dp_aux_dev_class);
> +	unregister_chrdev(drm_dev_major, "aux");
> +}
> +
> +MODULE_AUTHOR("Rafael Antognolli <rafael.antognolli@intel.com>");
> +MODULE_DESCRIPTION("DRM DP AUX /dev entries driver");
> +MODULE_LICENSE("GPL");

Doesn't match your license boilerplate.

> +
> +module_init(drm_dp_aux_dev_init);
> +module_exit(drm_dp_aux_dev_exit);
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 9535c5b..f3a2eb0 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -28,6 +28,7 @@
>  #include <linux/sched.h>
>  #include <linux/i2c.h>
>  #include <drm/drm_dp_helper.h>
> +#include <drm/drm_dp_aux_dev.h>
>  #include <drm/drmP.h>
>  
>  /**
> @@ -768,6 +769,9 @@ int drm_dp_aux_register(struct drm_dp_aux *aux)
>  	strlcpy(aux->ddc.name, aux->name ? aux->name : dev_name(aux->dev),
>  		sizeof(aux->ddc.name));
>  
> +
> +	drm_dp_aux_register_devnode(aux);
> +
>  	return i2c_add_adapter(&aux->ddc);
>  }
>  EXPORT_SYMBOL(drm_dp_aux_register);
> @@ -778,6 +782,7 @@ EXPORT_SYMBOL(drm_dp_aux_register);
>   */
>  void drm_dp_aux_unregister(struct drm_dp_aux *aux)
>  {
> +	drm_dp_aux_unregister_devnode(aux);
>  	i2c_del_adapter(&aux->ddc);
>  }
>  EXPORT_SYMBOL(drm_dp_aux_unregister);
> diff --git a/include/drm/drm_dp_aux_dev.h b/include/drm/drm_dp_aux_dev.h
> new file mode 100644
> index 0000000..77534e8
> --- /dev/null
> +++ b/include/drm/drm_dp_aux_dev.h
> @@ -0,0 +1,50 @@
> +/*
> + * 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>
> + *
> + */
> +
> +#ifndef _UAPI_LINUX_DRM_DP_AUX_DEV_
> +#define _UAPI_LINUX_DRM_DP_AUX_DEV_

Not uapi.

#ifndef DRM_DP_AUX_DEV_H
#define ...
would seem line enough.

> +
> +#ifdef CONFIG_DRM_DP_AUX_CHARDEV
> +
> +int drm_dp_aux_register_devnode(struct drm_dp_aux *aux);
> +int drm_dp_aux_unregister_devnode(struct drm_dp_aux *aux);
> +
> +#else
> +
> +static inline int drm_dp_aux_register_devnode(struct drm_dp_aux *aux)
> +{
> +	return 0;
> +}
> +
> +static inline int drm_dp_aux_unregister_devnode(struct drm_dp_aux *aux)
> +{
> +	return 0;
> +}
> +
> +#endif
> +
> +#endif
> -- 
> 2.4.3
> 
> _______________________________________________
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> dri-devel@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Ville Syrjälä
Intel OTC
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