drm: use anon-inode instead of relying on cdevs
DRM drivers share a common address_space across all character-devices of a
single DRM device. This allows simple buffer eviction and mapping-control.
However, DRM core currently waits for the first ->open() on any char-dev
to mark the underlying inode as backing inode of the device. This delayed
initialization causes ugly conditions all over the place:
if (dev->dev_mapping)
do_sth();
To avoid delayed initialization and to stop reusing the inode of the
char-dev, we allocate an anonymous inode for each DRM device and reset
filp->f_mapping to it on ->open().
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index 7f2af9a..147a84d 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -84,8 +84,6 @@
struct drm_minor *minor;
int retcode = 0;
int need_setup = 0;
- struct address_space *old_mapping;
- struct address_space *old_imapping;
minor = idr_find(&drm_minors_idr, minor_id);
if (!minor)
@@ -99,16 +97,9 @@
if (!dev->open_count++)
need_setup = 1;
- mutex_lock(&dev->struct_mutex);
- old_imapping = inode->i_mapping;
- old_mapping = dev->dev_mapping;
- if (old_mapping == NULL)
- dev->dev_mapping = &inode->i_data;
- /* ihold ensures nobody can remove inode with our i_data */
- ihold(container_of(dev->dev_mapping, struct inode, i_data));
- inode->i_mapping = dev->dev_mapping;
- filp->f_mapping = dev->dev_mapping;
- mutex_unlock(&dev->struct_mutex);
+
+ /* share address_space across all char-devs of a single device */
+ filp->f_mapping = dev->anon_inode->i_mapping;
retcode = drm_open_helper(inode, filp, dev);
if (retcode)
@@ -121,12 +112,6 @@
return 0;
err_undo:
- mutex_lock(&dev->struct_mutex);
- filp->f_mapping = old_imapping;
- inode->i_mapping = old_imapping;
- iput(container_of(dev->dev_mapping, struct inode, i_data));
- dev->dev_mapping = old_mapping;
- mutex_unlock(&dev->struct_mutex);
dev->open_count--;
return retcode;
}
@@ -434,7 +419,6 @@
drm_legacy_dma_takedown(dev);
- dev->dev_mapping = NULL;
mutex_unlock(&dev->struct_mutex);
drm_legacy_dev_reinit(dev);
@@ -549,9 +533,6 @@
}
}
- BUG_ON(dev->dev_mapping == NULL);
- iput(container_of(dev->dev_mapping, struct inode, i_data));
-
/* drop the reference held my the file priv */
if (file_priv->master)
drm_master_put(&file_priv->master);