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

[Rafael Antognolli <rafael.antognolli@intel.com>]

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;
+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++;
+	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);
+}
+
+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;
+	if (bytes_pending < 0)
+		return -EFAULT;
+
+	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;
+
+		res = drm_dp_dpcd_read(aux_dev->aux, *offset, localbuf, todo);
+		if (res <= 0) {
+			return num_bytes_processed ? num_bytes_processed : res;
+		}
+		if (__copy_to_user(buf + num_bytes_processed, localbuf, res)) {
+			return num_bytes_processed ?
+				num_bytes_processed : -EFAULT;
+		}
+		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;
+		}
+		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));
+
+	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");
+
+	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");
+	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");
+
+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_
+
+#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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