drm: Use a const drm_driver for legacy PCI devices

Now that the legacy PCI support code doesn't need to write to the
drm_driver structure, it can be treated as const through the whole DRM
core, unconditionally. This allows declaring the structure as const in
all drivers, removing one possible attack vector.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_drv.c

@@ -589,11 +589,7 @@ static int drm_dev_init(struct drm_device *dev,
 
 	kref_init(&dev->ref);
 	dev->dev = get_device(parent);
-#ifdef CONFIG_DRM_LEGACY
-	dev->driver = (struct drm_driver *)driver;
-#else
 	dev->driver = driver;
-#endif
 
 	INIT_LIST_HEAD(&dev->managed.resources);
 	spin_lock_init(&dev->managed.lock);

drivers/gpu/drm/drm_pci.c

@@ -201,7 +201,7 @@ static void drm_pci_agp_init(struct drm_device *dev)
 
 static int drm_get_pci_dev(struct pci_dev *pdev,
 			   const struct pci_device_id *ent,
-			   struct drm_driver *driver)
+			   const struct drm_driver *driver)
 {
 	struct drm_device *dev;
 	int ret;
@@ -255,7 +255,8 @@ static int drm_get_pci_dev(struct pci_dev *pdev,
  *
  * Return: 0 on success or a negative error code on failure.
  */
-int drm_legacy_pci_init(struct drm_driver *driver, struct pci_driver *pdriver)
+int drm_legacy_pci_init(const struct drm_driver *driver,
+			struct pci_driver *pdriver)
 {
 	struct pci_dev *pdev = NULL;
 	const struct pci_device_id *pid;
@@ -300,7 +301,8 @@ EXPORT_SYMBOL(drm_legacy_pci_init);
  * Unregister a DRM driver shadow-attached through drm_legacy_pci_init(). This
  * is deprecated and only used by dri1 drivers.
  */
-void drm_legacy_pci_exit(struct drm_driver *driver, struct pci_driver *pdriver)
+void drm_legacy_pci_exit(const struct drm_driver *driver,
+			 struct pci_driver *pdriver)
 {
 	struct drm_device *dev, *tmp;
 

include/drm/drm_device.h

@@ -76,11 +76,7 @@ struct drm_device {
 	} managed;
 
 	/** @driver: DRM driver managing the device */
-#ifdef CONFIG_DRM_LEGACY
-	struct drm_driver *driver;
-#else
 	const struct drm_driver *driver;
-#endif
 
 	/**
 	 * @dev_private:

include/drm/drm_legacy.h

@@ -198,8 +198,10 @@ struct drm_dma_handle *drm_pci_alloc(struct drm_device *dev, size_t size,
 				     size_t align);
 void drm_pci_free(struct drm_device *dev, struct drm_dma_handle *dmah);
 
-int drm_legacy_pci_init(struct drm_driver *driver, struct pci_driver *pdriver);
-void drm_legacy_pci_exit(struct drm_driver *driver, struct pci_driver *pdriver);
+int drm_legacy_pci_init(const struct drm_driver *driver,
+			struct pci_driver *pdriver);
+void drm_legacy_pci_exit(const struct drm_driver *driver,
+			 struct pci_driver *pdriver);
 
 #else
 
@@ -214,13 +216,13 @@ static inline void drm_pci_free(struct drm_device *dev,
 {
 }
 
-static inline int drm_legacy_pci_init(struct drm_driver *driver,
+static inline int drm_legacy_pci_init(const struct drm_driver *driver,
 				      struct pci_driver *pdriver)
 {
 	return -EINVAL;
 }
 
-static inline void drm_legacy_pci_exit(struct drm_driver *driver,
+static inline void drm_legacy_pci_exit(const struct drm_driver *driver,
 				       struct pci_driver *pdriver)
 {
 }