[RFC PATCH v3 2/3] accel: add dedicated minor for accelerator devices

[Oded Gabbay <ogabbay@kernel.org>]

The accelerator devices are exposed to user-space using a dedicated
major. In addition, they are represented in /dev with new, dedicated
device char names: /dev/accel/accel*. This is done to make sure any
user-space software that tries to open a graphic card won't open
the accelerator device by mistake.

The above implies that the minor numbering should be separated from
the rest of the DRM devices. However, to avoid code duplication, we
want the drm_minor structure to be able to represent the accelerator
device.

To achieve this, we add a new drm_minor* to drm_device that represents
the accelerator device. This pointer is initialized for drivers that
declare they handle compute accelerator, using a new driver feature
flag called DRIVER_COMPUTE_ACCEL. It is important to note that this
driver feature is mutually exclusive with DRIVER_RENDER. Devices that
want to expose both graphics and compute device char files should be
handled by two drivers that are connected using the auxiliary bus
framework.

In addition, we define a different IDR to handle the accelerators
minors. This is done to make the minor's index be identical to the
device index in /dev/. Any access to the IDR is done solely
by functions in accel_drv.c, as the IDR is define as static. The
DRM core functions call those functions in case they detect the minor's
type is DRM_MINOR_ACCEL.

We define a separate accel_open function (from drm_open) that the
accel drivers should set as their open callback function. Both these
functions eventually call the same drm_open_helper(), which had to be
changed to be non-static so it can be called from accel_drv.c.
accel_open() only partially duplicates drm_open as I removed some code
from it that handles legacy devices.

To help new drivers, I defined DEFINE_DRM_ACCEL_FOPS macro to easily
set the required function operations pointers structure.

Signed-off-by: Oded Gabbay <ogabbay@kernel.org>
---
Changes in v3:
 - Remove useless DRM_DEBUG("\n") at accel_stub_open()
 - Add function of accel_debugfs_init() as accel_debugfs_root is static
   member in drm_accel.c
 - Add DRM_ACCEL_FOPS and DEFINE_DRM_ACCEL_FOPS macros
 - Replace minor handling from xarray back to idr, as xarray doesn't handle
   well exchanging content of a NULL entry to non-NULL. This should be handled
   in a different patch that will either fix xarray code or change DRM minor
   init flow.
 - Make accel_minor_replace() to return void.

 drivers/accel/drm_accel.c  | 242 ++++++++++++++++++++++++++++++++++++-
 drivers/gpu/drm/drm_file.c |   2 +-
 include/drm/drm_accel.h    |  68 ++++++++++-
 include/drm/drm_device.h   |   3 +
 include/drm/drm_drv.h      |   8 ++
 include/drm/drm_file.h     |  21 +++-
 6 files changed, 340 insertions(+), 4 deletions(-)

diff --git a/drivers/accel/drm_accel.c b/drivers/accel/drm_accel.c
index 943d960ddefc..05167c929866 100644
--- a/drivers/accel/drm_accel.c
+++ b/drivers/accel/drm_accel.c
@@ -8,14 +8,25 @@

 #include <linux/debugfs.h>
 #include <linux/device.h>
+#include <linux/xarray.h>

 #include <drm/drm_accel.h>
+#include <drm/drm_debugfs.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_file.h>
 #include <drm/drm_ioctl.h>
 #include <drm/drm_print.h>

+static DEFINE_SPINLOCK(accel_minor_lock);
+static struct idr accel_minors_idr;
+
 static struct dentry *accel_debugfs_root;
 static struct class *accel_class;

+static struct device_type accel_sysfs_device_minor = {
+	.name = "accel_minor"
+};
+
 static char *accel_devnode(struct device *dev, umode_t *mode)
 {
 	return kasprintf(GFP_KERNEL, "accel/%s", dev_name(dev));
@@ -40,9 +51,235 @@ static void accel_sysfs_destroy(void)
 	accel_class = NULL;
 }

+static int accel_name_info(struct seq_file *m, void *data)
+{
+	struct drm_info_node *node = (struct drm_info_node *) m->private;
+	struct drm_minor *minor = node->minor;
+	struct drm_device *dev = minor->dev;
+	struct drm_master *master;
+
+	mutex_lock(&dev->master_mutex);
+	master = dev->master;
+	seq_printf(m, "%s", dev->driver->name);
+	if (dev->dev)
+		seq_printf(m, " dev=%s", dev_name(dev->dev));
+	if (master && master->unique)
+		seq_printf(m, " master=%s", master->unique);
+	if (dev->unique)
+		seq_printf(m, " unique=%s", dev->unique);
+	seq_puts(m, "\n");
+	mutex_unlock(&dev->master_mutex);
+
+	return 0;
+}
+
+static const struct drm_info_list accel_debugfs_list[] = {
+	{"name", accel_name_info, 0}
+};
+#define ACCEL_DEBUGFS_ENTRIES ARRAY_SIZE(accel_debugfs_list)
+
+/**
+ * accel_debugfs_init() - Initialize debugfs for accel minor
+ * @minor: Pointer to the drm_minor instance.
+ * @minor_id: The minor's id
+ *
+ * This function initializes the drm minor's debugfs members and creates
+ * a root directory for the minor in debugfs. It also creates common files
+ * for accelerators and calls the driver's debugfs init callback.
+ */
+void accel_debugfs_init(struct drm_minor *minor, int minor_id)
+{
+	struct drm_device *dev = minor->dev;
+	char name[64];
+
+	INIT_LIST_HEAD(&minor->debugfs_list);
+	mutex_init(&minor->debugfs_lock);
+	sprintf(name, "%d", minor_id);
+	minor->debugfs_root = debugfs_create_dir(name, accel_debugfs_root);
+
+	drm_debugfs_create_files(accel_debugfs_list, ACCEL_DEBUGFS_ENTRIES,
+				 minor->debugfs_root, minor);
+
+	if (dev->driver->debugfs_init)
+		dev->driver->debugfs_init(minor);
+}
+
+/**
+ * accel_set_device_instance_params() - Set some device parameters for accel device
+ * @kdev: Pointer to the device instance.
+ * @index: The minor's index
+ *
+ * This function creates the dev_t of the device using the accel major and
+ * the device's minor number. In addition, it sets the class and type of the
+ * device instance to the accel sysfs class and device type, respectively.
+ */
+void accel_set_device_instance_params(struct device *kdev, int index)
+{
+	kdev->devt = MKDEV(ACCEL_MAJOR, index);
+	kdev->class = accel_class;
+	kdev->type = &accel_sysfs_device_minor;
+}
+
+/**
+ * accel_minor_alloc() - Allocates a new accel minor
+ *
+ * This function access the accel minors idr and allocates from it
+ * a new id to represent a new accel minor
+ *
+ * Return: A new id on success or error code in case idr_alloc failed
+ */
+int accel_minor_alloc(void)
+{
+	unsigned long flags;
+	int r;
+
+	spin_lock_irqsave(&accel_minor_lock, flags);
+	r = idr_alloc(&accel_minors_idr, NULL, 0, ACCEL_MAX_MINORS, GFP_NOWAIT);
+	spin_unlock_irqrestore(&accel_minor_lock, flags);
+
+	return r;
+}
+
+/**
+ * accel_minor_remove() - Remove an accel minor
+ * @index: The minor id to remove.
+ *
+ * This function access the accel minors idr and removes from
+ * it the member with the id that is passed to this function.
+ */
+void accel_minor_remove(int index)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&accel_minor_lock, flags);
+	idr_remove(&accel_minors_idr, index);
+	spin_unlock_irqrestore(&accel_minor_lock, flags);
+}
+
+/**
+ * accel_minor_replace() - Replace minor pointer in accel minors idr.
+ * @minor: Pointer to the new minor.
+ * @index: The minor id to replace.
+ *
+ * This function access the accel minors idr structure and replaces the pointer
+ * that is associated with an existing id. Because the minor pointer can be
+ * NULL, we need to explicitly pass the index.
+ *
+ * Return: 0 for success, negative value for error
+ */
+void accel_minor_replace(struct drm_minor *minor, int index)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&accel_minor_lock, flags);
+	idr_replace(&accel_minors_idr, minor, index);
+	spin_unlock_irqrestore(&accel_minor_lock, flags);
+}
+
+/*
+ * Looks up the given minor-ID and returns the respective DRM-minor object. The
+ * refence-count of the underlying device is increased so you must release this
+ * object with accel_minor_release().
+ *
+ * The object can be only a drm_minor that represents an accel device.
+ *
+ * As long as you hold this minor, it is guaranteed that the object and the
+ * minor->dev pointer will stay valid! However, the device may get unplugged and
+ * unregistered while you hold the minor.
+ */
+static struct drm_minor *accel_minor_acquire(unsigned int minor_id)
+{
+	struct drm_minor *minor;
+	unsigned long flags;
+
+	spin_lock_irqsave(&accel_minor_lock, flags);
+	minor = idr_find(&accel_minors_idr, minor_id);
+	if (minor)
+		drm_dev_get(minor->dev);
+	spin_unlock_irqrestore(&accel_minor_lock, flags);
+
+	if (!minor) {
+		return ERR_PTR(-ENODEV);
+	} else if (drm_dev_is_unplugged(minor->dev)) {
+		drm_dev_put(minor->dev);
+		return ERR_PTR(-ENODEV);
+	}
+
+	return minor;
+}
+
+static void accel_minor_release(struct drm_minor *minor)
+{
+	drm_dev_put(minor->dev);
+}
+
+/**
+ * accel_open - open method for ACCEL file
+ * @inode: device inode
+ * @filp: file pointer.
+ *
+ * This function must be used by drivers as their &file_operations.open method.
+ * It looks up the correct ACCEL device and instantiates all the per-file
+ * resources for it. It also calls the &drm_driver.open driver callback.
+ *
+ * Return: 0 on success or negative errno value on failure.
+ */
+int accel_open(struct inode *inode, struct file *filp)
+{
+	struct drm_device *dev;
+	struct drm_minor *minor;
+	int retcode;
+
+	minor = accel_minor_acquire(iminor(inode));
+	if (IS_ERR(minor))
+		return PTR_ERR(minor);
+
+	dev = minor->dev;
+
+	atomic_fetch_inc(&dev->open_count);
+
+	/* share address_space across all char-devs of a single device */
+	filp->f_mapping = dev->anon_inode->i_mapping;
+
+	retcode = drm_open_helper(filp, minor);
+	if (retcode)
+		goto err_undo;
+
+	return 0;
+
+err_undo:
+	atomic_dec(&dev->open_count);
+	accel_minor_release(minor);
+	return retcode;
+}
+EXPORT_SYMBOL_GPL(accel_open);
+
 static int accel_stub_open(struct inode *inode, struct file *filp)
 {
-	return -EOPNOTSUPP;
+	const struct file_operations *new_fops;
+	struct drm_minor *minor;
+	int err;
+
+	minor = accel_minor_acquire(iminor(inode));
+	if (IS_ERR(minor))
+		return PTR_ERR(minor);
+
+	new_fops = fops_get(minor->dev->driver->fops);
+	if (!new_fops) {
+		err = -ENODEV;
+		goto out;
+	}
+
+	replace_fops(filp, new_fops);
+	if (filp->f_op->open)
+		err = filp->f_op->open(inode, filp);
+	else
+		err = 0;
+
+out:
+	accel_minor_release(minor);
+
+	return err;
 }

 static const struct file_operations accel_stub_fops = {
@@ -56,12 +293,15 @@ void accel_core_exit(void)
 	unregister_chrdev(ACCEL_MAJOR, "accel");
 	debugfs_remove(accel_debugfs_root);
 	accel_sysfs_destroy();
+	idr_destroy(&accel_minors_idr);
 }

 int __init accel_core_init(void)
 {
 	int ret;

+	idr_init(&accel_minors_idr);
+
 	ret = accel_sysfs_init();
 	if (ret < 0) {
 		DRM_ERROR("Cannot create ACCEL class: %d\n", ret);
diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
index a8b4d918e9a3..64b4a3a87fbb 100644
--- a/drivers/gpu/drm/drm_file.c
+++ b/drivers/gpu/drm/drm_file.c
@@ -326,7 +326,7 @@ static int drm_cpu_valid(void)
  * Creates and initializes a drm_file structure for the file private data in \p
  * filp and add it into the double linked list in \p dev.
  */
-static int drm_open_helper(struct file *filp, struct drm_minor *minor)
+int drm_open_helper(struct file *filp, struct drm_minor *minor)
 {
 	struct drm_device *dev = minor->dev;
 	struct drm_file *priv;
diff --git a/include/drm/drm_accel.h b/include/drm/drm_accel.h
index 31b42d3d6a15..b0c20367faad 100644
--- a/include/drm/drm_accel.h
+++ b/include/drm/drm_accel.h
@@ -8,12 +8,56 @@
 #ifndef DRM_ACCEL_H_
 #define DRM_ACCEL_H_

-#define ACCEL_MAJOR     261
+#include <drm/drm_file.h>
+
+#define ACCEL_MAJOR		261
+#define ACCEL_MAX_MINORS	256
+
+/**
+ * DRM_ACCEL_FOPS - Default drm accelerators file operations
+ *
+ * This macro provides a shorthand for setting the accelerator file ops in the
+ * &file_operations structure.  If all you need are the default ops, use
+ * DEFINE_DRM_ACCEL_FOPS instead.
+ */
+#define DRM_ACCEL_FOPS \
+	.open		= accel_open,\
+	.release	= drm_release,\
+	.unlocked_ioctl	= drm_ioctl,\
+	.compat_ioctl	= drm_compat_ioctl,\
+	.poll		= drm_poll,\
+	.read		= drm_read,\
+	.llseek		= noop_llseek
+
+/**
+ * DEFINE_DRM_ACCEL_FOPS() - macro to generate file operations for accelerators drivers
+ * @name: name for the generated structure
+ *
+ * This macro autogenerates a suitable &struct file_operations for accelerators based
+ * drivers, which can be assigned to &drm_driver.fops. Note that this structure
+ * cannot be shared between drivers, because it contains a reference to the
+ * current module using THIS_MODULE.
+ *
+ * Note that the declaration is already marked as static - if you need a
+ * non-static version of this you're probably doing it wrong and will break the
+ * THIS_MODULE reference by accident.
+ */
+#define DEFINE_DRM_ACCEL_FOPS(name) \
+	static const struct file_operations name = {\
+		.owner		= THIS_MODULE,\
+		DRM_ACCEL_FOPS,\
+	}

 #if IS_ENABLED(CONFIG_DRM_ACCEL)

 void accel_core_exit(void);
 int accel_core_init(void);
+void accel_minor_remove(int index);
+int accel_minor_alloc(void);
+void accel_minor_replace(struct drm_minor *minor, int index);
+void accel_set_device_instance_params(struct device *kdev, int index);
+int accel_open(struct inode *inode, struct file *filp);
+void accel_debugfs_init(struct drm_minor *minor, int minor_id);

 #else

@@ -23,9 +67,31 @@ static inline void accel_core_exit(void)

 static inline int __init accel_core_init(void)
 {
+	/* Return 0 to allow drm_core_init to complete successfully */
 	return 0;
 }

+static inline void accel_minor_remove(int index)
+{
+}
+
+static inline int accel_minor_alloc(void)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline void accel_minor_replace(struct drm_minor *minor, int index)
+{
+}
+
+static inline void accel_set_device_instance_params(struct device *kdev, int index)
+{
+}
+
+static inline void accel_debugfs_init(struct drm_minor *minor, int minor_id)
+{
+
+
 #endif /* IS_ENABLED(CONFIG_DRM_ACCEL) */

 #endif /* DRM_ACCEL_H_ */
diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h
index 9923c7a6885e..933ce2048e20 100644
--- a/include/drm/drm_device.h
+++ b/include/drm/drm_device.h
@@ -93,6 +93,9 @@ struct drm_device {
 	/** @render: Render node */
 	struct drm_minor *render;

+	/** @accel: Compute Acceleration node */
+	struct drm_minor *accel;
+
 	/**
 	 * @registered:
 	 *
diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
index f6159acb8856..706e68ca5116 100644
--- a/include/drm/drm_drv.h
+++ b/include/drm/drm_drv.h
@@ -94,6 +94,14 @@ enum drm_driver_feature {
 	 * synchronization of command submission.
 	 */
 	DRIVER_SYNCOBJ_TIMELINE         = BIT(6),
+	/**
+	 * @DRIVER_COMPUTE_ACCEL:
+	 *
+	 * Driver supports compute acceleration devices. This flag is mutually exclusive with
+	 * @DRIVER_RENDER and @DRIVER_MODESET. Devices that support both graphics and compute
+	 * acceleration should be handled by two drivers that are connected using auxiliry bus.
+	 */
+	DRIVER_COMPUTE_ACCEL            = BIT(7),

 	/* IMPORTANT: Below are all the legacy flags, add new ones above. */

diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
index d780fd151789..0d1f853092ab 100644
--- a/include/drm/drm_file.h
+++ b/include/drm/drm_file.h
@@ -51,11 +51,15 @@ struct file;

 /* Note that the order of this enum is ABI (it determines
  * /dev/dri/renderD* numbers).
+ *
+ * Setting DRM_MINOR_ACCEL to 32 gives enough space for more drm minors to
+ * be implemented before we hit any future
  */
 enum drm_minor_type {
 	DRM_MINOR_PRIMARY,
 	DRM_MINOR_CONTROL,
 	DRM_MINOR_RENDER,
+	DRM_MINOR_ACCEL = 32,
 };

 /**
@@ -70,7 +74,7 @@ enum drm_minor_type {
 struct drm_minor {
 	/* private: */
 	int index;			/* Minor device number */
-	int type;                       /* Control or render */
+	int type;                       /* Control or render or accel */
 	struct device *kdev;		/* Linux device */
 	struct drm_device *dev;

@@ -397,7 +401,22 @@ static inline bool drm_is_render_client(const struct drm_file *file_priv)
 	return file_priv->minor->type == DRM_MINOR_RENDER;
 }

+/**
+ * drm_is_accel_client - is this an open file of the compute acceleration node
+ * @file_priv: DRM file
+ *
+ * Returns true if this is an open file of the compute acceleration node, i.e.
+ * &drm_file.minor of @file_priv is a accel minor.
+ *
+ * See also the :ref:`section on accel nodes <drm_accel_node>`.
+ */
+static inline bool drm_is_accel_client(const struct drm_file *file_priv)
+{
+	return file_priv->minor->type == DRM_MINOR_ACCEL;
+}
+
 int drm_open(struct inode *inode, struct file *filp);
+int drm_open_helper(struct file *filp, struct drm_minor *minor);
 ssize_t drm_read(struct file *filp, char __user *buffer,
 		 size_t count, loff_t *offset);
 int drm_release(struct inode *inode, struct file *filp);
--
2.25.1