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>

15 files changed, 44 insertions, 54 deletions

diff --git a/drivers/gpu/drm/ast/ast_ttm.c b/drivers/gpu/drm/ast/ast_ttm.c
index 4ea9b17ac17a..2b491539e60c 100644
--- a/drivers/gpu/drm/ast/ast_ttm.c
+++ b/drivers/gpu/drm/ast/ast_ttm.c
@@ -324,7 +324,7 @@ int ast_bo_create(struct drm_device *dev, int size, int align,
         }
 
         astbo->bo.bdev = &ast->ttm.bdev;
-        astbo->bo.bdev->dev_mapping = dev->dev_mapping;
+        astbo->bo.bdev->dev_mapping = dev->anon_inode->i_mapping;
 
         ast_ttm_placement(astbo, TTM_PL_FLAG_VRAM | TTM_PL_FLAG_SYSTEM);
 
diff --git a/drivers/gpu/drm/bochs/bochs_mm.c b/drivers/gpu/drm/bochs/bochs_mm.c
index ce6858765b37..2d8546d7b4af 100644
--- a/drivers/gpu/drm/bochs/bochs_mm.c
+++ b/drivers/gpu/drm/bochs/bochs_mm.c
@@ -359,7 +359,7 @@ static int bochs_bo_create(struct drm_device *dev, int size, int align,
         }
 
         bochsbo->bo.bdev = &bochs->ttm.bdev;
-        bochsbo->bo.bdev->dev_mapping = dev->dev_mapping;
+        bochsbo->bo.bdev->dev_mapping = dev->anon_inode->i_mapping;
 
         bochs_ttm_placement(bochsbo, TTM_PL_FLAG_VRAM | TTM_PL_FLAG_SYSTEM);
 
diff --git a/drivers/gpu/drm/cirrus/cirrus_ttm.c b/drivers/gpu/drm/cirrus/cirrus_ttm.c
index 8b37c25ff9bd..efcbd70a8774 100644
--- a/drivers/gpu/drm/cirrus/cirrus_ttm.c
+++ b/drivers/gpu/drm/cirrus/cirrus_ttm.c
@@ -329,7 +329,7 @@ int cirrus_bo_create(struct drm_device *dev, int size, int align,
         }
 
         cirrusbo->bo.bdev = &cirrus->ttm.bdev;
-        cirrusbo->bo.bdev->dev_mapping = dev->dev_mapping;
+        cirrusbo->bo.bdev->dev_mapping = dev->anon_inode->i_mapping;
 
         cirrus_ttm_placement(cirrusbo, TTM_PL_FLAG_VRAM | TTM_PL_FLAG_SYSTEM);
 
diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index 7f2af9aca038..147a84d9da9b 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -84,8 +84,6 @@ int drm_open(struct inode *inode, struct file *filp)
         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 @@ int drm_open(struct inode *inode, struct file *filp)
 
         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 @@ int drm_open(struct inode *inode, struct file *filp)
         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 @@ int drm_lastclose(struct drm_device * dev)
 
         drm_legacy_dma_takedown(dev);
 
-        dev->dev_mapping = NULL;
         mutex_unlock(&dev->struct_mutex);
 
         drm_legacy_dev_reinit(dev);
@@ -549,9 +533,6 @@ int drm_release(struct inode *inode, struct file *filp)
                 }
         }
 
-        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);
diff --git a/drivers/gpu/drm/drm_stub.c b/drivers/gpu/drm/drm_stub.c
index f2903d7e3d8e..04c25cedd4c1 100644
--- a/drivers/gpu/drm/drm_stub.c
+++ b/drivers/gpu/drm/drm_stub.c
@@ -526,8 +526,15 @@ struct drm_device *drm_dev_alloc(struct drm_driver *driver,
         mutex_init(&dev->struct_mutex);
         mutex_init(&dev->ctxlist_mutex);
 
-        if (drm_ht_create(&dev->map_hash, 12))
+        dev->anon_inode = drm_fs_inode_new();
+        if (IS_ERR(dev->anon_inode)) {
+                ret = PTR_ERR(dev->anon_inode);
+                DRM_ERROR("Cannot allocate anonymous inode: %d\n", ret);
                 goto err_free;
+        }
+
+        if (drm_ht_create(&dev->map_hash, 12))
+                goto err_inode;
 
         ret = drm_ctxbitmap_init(dev);
         if (ret) {
@@ -549,6 +556,8 @@ err_ctxbitmap:
         drm_ctxbitmap_cleanup(dev);
 err_ht:
         drm_ht_remove(&dev->map_hash);
+err_inode:
+        drm_fs_inode_free(dev->anon_inode);
 err_free:
         kfree(dev);
         return NULL;
@@ -576,6 +585,7 @@ void drm_dev_free(struct drm_device *dev)
 
         drm_ctxbitmap_cleanup(dev);
         drm_ht_remove(&dev->map_hash);
+        drm_fs_inode_free(dev->anon_inode);
 
         kfree(dev->devname);
         kfree(dev);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 3618bb0cda0a..928e15bb2cf7 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1508,7 +1508,8 @@ i915_gem_release_mmap(struct drm_i915_gem_object *obj)
         if (!obj->fault_mappable)
                 return;
 
-        drm_vma_node_unmap(&obj->base.vma_node, obj->base.dev->dev_mapping);
+        drm_vma_node_unmap(&obj->base.vma_node,
+                           obj->base.dev->anon_inode->i_mapping);
         obj->fault_mappable = false;
 }
 
diff --git a/drivers/gpu/drm/mgag200/mgag200_ttm.c b/drivers/gpu/drm/mgag200/mgag200_ttm.c
index adb5166a5dfd..c1c2cb608ab3 100644
--- a/drivers/gpu/drm/mgag200/mgag200_ttm.c
+++ b/drivers/gpu/drm/mgag200/mgag200_ttm.c
@@ -324,7 +324,7 @@ int mgag200_bo_create(struct drm_device *dev, int size, int align,
         }
 
         mgabo->bo.bdev = &mdev->ttm.bdev;
-        mgabo->bo.bdev->dev_mapping = dev->dev_mapping;
+        mgabo->bo.bdev->dev_mapping = dev->anon_inode->i_mapping;
 
         mgag200_ttm_placement(mgabo, TTM_PL_FLAG_VRAM | TTM_PL_FLAG_SYSTEM);
 
diff --git a/drivers/gpu/drm/nouveau/nouveau_gem.c b/drivers/gpu/drm/nouveau/nouveau_gem.c
index 27c3fd89e8ce..5b193b898f5a 100644
--- a/drivers/gpu/drm/nouveau/nouveau_gem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_gem.c
@@ -228,7 +228,7 @@ nouveau_gem_ioctl_new(struct drm_device *dev, void *data,
         struct nouveau_bo *nvbo = NULL;
         int ret = 0;
 
-        drm->ttm.bdev.dev_mapping = drm->dev->dev_mapping;
+        drm->ttm.bdev.dev_mapping = drm->dev->anon_inode->i_mapping;
 
         if (!pfb->memtype_valid(pfb, req->info.tile_flags)) {
                 NV_ERROR(cli, "bad page flags: 0x%08x\n", req->info.tile_flags);
diff --git a/drivers/gpu/drm/omapdrm/omap_gem.c b/drivers/gpu/drm/omapdrm/omap_gem.c
index 5aec3e81fe24..c8d972763889 100644
--- a/drivers/gpu/drm/omapdrm/omap_gem.c
+++ b/drivers/gpu/drm/omapdrm/omap_gem.c
@@ -153,24 +153,24 @@ static struct {
 static void evict_entry(struct drm_gem_object *obj,
                 enum tiler_fmt fmt, struct usergart_entry *entry)
 {
-        if (obj->dev->dev_mapping) {
-                struct omap_gem_object *omap_obj = to_omap_bo(obj);
-                int n = usergart[fmt].height;
-                size_t size = PAGE_SIZE * n;
-                loff_t off = mmap_offset(obj) +
-                                (entry->obj_pgoff << PAGE_SHIFT);
-                const int m = 1 + ((omap_obj->width << fmt) / PAGE_SIZE);
-                if (m > 1) {
-                        int i;
-                        /* if stride > than PAGE_SIZE then sparse mapping: */
-                        for (i = n; i > 0; i--) {
-                                unmap_mapping_range(obj->dev->dev_mapping,
-                                                off, PAGE_SIZE, 1);
-                                off += PAGE_SIZE * m;
-                        }
-                } else {
-                        unmap_mapping_range(obj->dev->dev_mapping, off, size, 1);
+        struct omap_gem_object *omap_obj = to_omap_bo(obj);
+        int n = usergart[fmt].height;
+        size_t size = PAGE_SIZE * n;
+        loff_t off = mmap_offset(obj) +
+                        (entry->obj_pgoff << PAGE_SHIFT);
+        const int m = 1 + ((omap_obj->width << fmt) / PAGE_SIZE);
+
+        if (m > 1) {
+                int i;
+                /* if stride > than PAGE_SIZE then sparse mapping: */
+                for (i = n; i > 0; i--) {
+                        unmap_mapping_range(obj->dev->anon_inode->i_mapping,
+                                            off, PAGE_SIZE, 1);
+                        off += PAGE_SIZE * m;
                 }
+        } else {
+                unmap_mapping_range(obj->dev->anon_inode->i_mapping,
+                                    off, size, 1);
         }
 
         entry->obj = NULL;
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");
diff --git a/drivers/gpu/drm/radeon/radeon_object.c b/drivers/gpu/drm/radeon/radeon_object.c
index ca79431b2c1c..6a7f3c6ffbbe 100644
--- a/drivers/gpu/drm/radeon/radeon_object.c
+++ b/drivers/gpu/drm/radeon/radeon_object.c
@@ -145,7 +145,7 @@ int radeon_bo_create(struct radeon_device *rdev,
 
         size = ALIGN(size, PAGE_SIZE);
 
-        rdev->mman.bdev.dev_mapping = rdev->ddev->dev_mapping;
+        rdev->mman.bdev.dev_mapping = rdev->ddev->anon_inode->i_mapping;
         if (kernel) {
                 type = ttm_bo_type_kernel;
         } else if (sg) {
diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c b/drivers/gpu/drm/radeon/radeon_ttm.c
index 60dfce889ecf..4663fbcfda28 100644
--- a/drivers/gpu/drm/radeon/radeon_ttm.c
+++ b/drivers/gpu/drm/radeon/radeon_ttm.c
@@ -745,7 +745,7 @@ int radeon_ttm_init(struct radeon_device *rdev)
         }
         DRM_INFO("radeon: %uM of GTT memory ready.\n",
                  (unsigned)(rdev->mc.gtt_size / (1024 * 1024)));
-        rdev->mman.bdev.dev_mapping = rdev->ddev->dev_mapping;
+        rdev->mman.bdev.dev_mapping = rdev->ddev->anon_inode->i_mapping;
 
         r = radeon_ttm_debugfs_init(rdev);
         if (r) {
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
index 0083cbf99edf..df4b03e035bc 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
@@ -969,7 +969,7 @@ static int vmw_driver_open(struct drm_device *dev, struct drm_file *file_priv)
                 goto out_no_shman;
 
         file_priv->driver_priv = vmw_fp;
-        dev_priv->bdev.dev_mapping = dev->dev_mapping;
+        dev_priv->bdev.dev_mapping = dev->anon_inode->i_mapping;
 
         return 0;
 
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 04a7f31301f8..3227b716ffdf 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -1183,7 +1183,7 @@ struct drm_device {
         struct drm_sg_mem *sg;  /**< Scatter gather memory */
         unsigned int num_crtcs;                  /**< Number of CRTCs on this device */
         void *dev_private;              /**< device private data */
-        struct address_space *dev_mapping;
+        struct inode *anon_inode;
         struct drm_sigdata sigdata;        /**< For block_all_signals */
         sigset_t sigmask;