drm: add minor-lookup/release helpers

Instead of accessing drm_minors_idr directly, this adds a small helper to
hide the internals. This will help us later to remove the drm_global_mutex
requirement for minor-lookup.

Furthermore, this also makes sure that minor->dev is always valid and
takes a reference-count to the device as long as the minor is used in an
open-file. This way, "struct file*"->private_data->dev is guaranteed to be
valid (which it has to, as we cannot reset it).

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 27 insertions, 23 deletions

diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index 6466cb5d8b1f..79478191404a 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -79,23 +79,22 @@ static int drm_setup(struct drm_device * dev)
  */
 int drm_open(struct inode *inode, struct file *filp)
 {
-        struct drm_device *dev = NULL;
-        int minor_id = iminor(inode);
+        struct drm_device *dev;
         struct drm_minor *minor;
-        int retcode = 0;
+        int retcode;
         int need_setup = 0;
         struct address_space *old_mapping;
         struct address_space *old_imapping;
 
-        minor = idr_find(&drm_minors_idr, minor_id);
-        if (!minor)
-                return -ENODEV;
-
-        if (!(dev = minor->dev))
-                return -ENODEV;
+        minor = drm_minor_acquire(iminor(inode));
+        if (IS_ERR(minor))
+                return PTR_ERR(minor);
 
-        if (drm_device_is_unplugged(dev))
-                return -ENODEV;
+        dev = minor->dev;
+        if (drm_device_is_unplugged(dev)) {
+                retcode = -ENODEV;
+                goto err_release;
+        }
 
         if (!dev->open_count++)
                 need_setup = 1;
@@ -128,6 +127,8 @@ err_undo:
         dev->dev_mapping = old_mapping;
         mutex_unlock(&dev->struct_mutex);
         dev->open_count--;
+err_release:
+        drm_minor_release(minor);
         return retcode;
 }
 EXPORT_SYMBOL(drm_open);
@@ -143,33 +144,33 @@ EXPORT_SYMBOL(drm_open);
  */
 int drm_stub_open(struct inode *inode, struct file *filp)
 {
-        struct drm_device *dev = NULL;
+        struct drm_device *dev;
         struct drm_minor *minor;
-        int minor_id = iminor(inode);
         int err = -ENODEV;
         const struct file_operations *new_fops;
 
         DRM_DEBUG("\n");
 
         mutex_lock(&drm_global_mutex);
-        minor = idr_find(&drm_minors_idr, minor_id);
-        if (!minor)
-                goto out;
-
-        if (!(dev = minor->dev))
-                goto out;
+        minor = drm_minor_acquire(iminor(inode));
+        if (IS_ERR(minor))
+                goto out_unlock;
 
+        dev = minor->dev;
         if (drm_device_is_unplugged(dev))
-                goto out;
+                goto out_release;
 
         new_fops = fops_get(dev->driver->fops);
         if (!new_fops)
-                goto out;
+                goto out_release;
 
         replace_fops(filp, new_fops);
         if (filp->f_op->open)
                 err = filp->f_op->open(inode, filp);
-out:
+
+out_release:
+        drm_minor_release(minor);
+out_unlock:
         mutex_unlock(&drm_global_mutex);
         return err;
 }
@@ -453,7 +454,8 @@ int drm_lastclose(struct drm_device * dev)
 int drm_release(struct inode *inode, struct file *filp)
 {
         struct drm_file *file_priv = filp->private_data;
-        struct drm_device *dev = file_priv->minor->dev;
+        struct drm_minor *minor = file_priv->minor;
+        struct drm_device *dev = minor->dev;
         int retcode = 0;
 
         mutex_lock(&drm_global_mutex);
@@ -575,6 +577,8 @@ int drm_release(struct inode *inode, struct file *filp)
         }
         mutex_unlock(&drm_global_mutex);
 
+        drm_minor_release(minor);
+
         return retcode;
 }
 EXPORT_SYMBOL(drm_release);