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>

2 files changed, 2 insertions, 4 deletions

diff --git a/drivers/gpu/drm/qxl/qxl_object.c b/drivers/gpu/drm/qxl/qxl_object.c
index 8691c76c5ef0..7e20c21b0879 100644
--- a/drivers/gpu/drm/qxl/qxl_object.c
+++ b/drivers/gpu/drm/qxl/qxl_object.c
@@ -82,8 +82,7 @@ int qxl_bo_create(struct qxl_device *qdev,
         enum ttm_bo_type type;
         int r;
 
-        if (unlikely(qdev->mman.bdev.dev_mapping == NULL))
-                qdev->mman.bdev.dev_mapping = qdev->ddev->dev_mapping;
+        qdev->mman.bdev.dev_mapping = qdev->ddev->anon_inode->i_mapping;
         if (kernel)
                 type = ttm_bo_type_kernel;
         else
diff --git a/drivers/gpu/drm/qxl/qxl_ttm.c b/drivers/gpu/drm/qxl/qxl_ttm.c
index c7e7e6590c2b..78cbc40a8efb 100644
--- a/drivers/gpu/drm/qxl/qxl_ttm.c
+++ b/drivers/gpu/drm/qxl/qxl_ttm.c
@@ -518,8 +518,7 @@ int qxl_ttm_init(struct qxl_device *qdev)
                  ((unsigned)num_io_pages * PAGE_SIZE) / (1024 * 1024));
         DRM_INFO("qxl: %uM of Surface memory size\n",
                  (unsigned)qdev->surfaceram_size / (1024 * 1024));
-        if (unlikely(qdev->mman.bdev.dev_mapping == NULL))
-                qdev->mman.bdev.dev_mapping = qdev->ddev->dev_mapping;
+        qdev->mman.bdev.dev_mapping = qdev->ddev->anon_inode->i_mapping;
         r = qxl_ttm_debugfs_init(qdev);
         if (r) {
                 DRM_ERROR("Failed to init debugfs\n");