drm: Allow const struct drm_driver

It's nice if a big function/ioctl table like this is const. Only
downside here is that we need a few more #ifdef to paper over the
differences when CONFIG_DRM_LEGACY is enabled. Maybe provides more
motivation to sunset that horror show :-)

v2:
- Fix super important checkpatch warning (Sam)
- Update the kerneldoc example too (Sam)
Acked-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20201104100425.1922351-4-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_drv.c

@@ -284,7 +284,7 @@ void drm_minor_release(struct drm_minor *minor)
  *		struct clk *pclk;
  *	};
  *
- *	static struct drm_driver driver_drm_driver = {
+ *	static const struct drm_driver driver_drm_driver = {
  *		[...]
  *	};
  *
@@ -574,7 +574,7 @@ static void drm_dev_init_release(struct drm_device *dev, void *res)
 }
 
 static int drm_dev_init(struct drm_device *dev,
-			struct drm_driver *driver,
+			const struct drm_driver *driver,
 			struct device *parent)
 {
 	int ret;
@@ -589,7 +589,11 @@ 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);
@@ -663,7 +667,7 @@ static void devm_drm_dev_init_release(void *data)
 
 static int devm_drm_dev_init(struct device *parent,
 			     struct drm_device *dev,
-			     struct drm_driver *driver)
+			     const struct drm_driver *driver)
 {
 	int ret;
 
@@ -678,7 +682,8 @@ static int devm_drm_dev_init(struct device *parent,
 	return ret;
 }
 
-void *__devm_drm_dev_alloc(struct device *parent, struct drm_driver *driver,
+void *__devm_drm_dev_alloc(struct device *parent,
+			   const struct drm_driver *driver,
 			   size_t size, size_t offset)
 {
 	void *container;
@@ -713,7 +718,7 @@ EXPORT_SYMBOL(__devm_drm_dev_alloc);
  * RETURNS:
  * Pointer to new DRM device, or ERR_PTR on failure.
  */
-struct drm_device *drm_dev_alloc(struct drm_driver *driver,
+struct drm_device *drm_dev_alloc(const struct drm_driver *driver,
 				 struct device *parent)
 {
 	struct drm_device *dev;
@@ -858,7 +863,7 @@ static void remove_compat_control_link(struct drm_device *dev)
  */
 int drm_dev_register(struct drm_device *dev, unsigned long flags)
 {
-	struct drm_driver *driver = dev->driver;
+	const struct drm_driver *driver = dev->driver;
 	int ret;
 
 	if (!driver->load)

include/drm/drm_device.h

@@ -83,7 +83,11 @@ 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_drv.h

@@ -513,7 +513,8 @@ struct drm_driver {
 #endif
 };
 
-void *__devm_drm_dev_alloc(struct device *parent, struct drm_driver *driver,
+void *__devm_drm_dev_alloc(struct device *parent,
+			   const struct drm_driver *driver,
 			   size_t size, size_t offset);
 
 /**
@@ -546,7 +547,7 @@ void *__devm_drm_dev_alloc(struct device *parent, struct drm_driver *driver,
 	((type *) __devm_drm_dev_alloc(parent, driver, sizeof(type), \
 				       offsetof(type, member)))
 
-struct drm_device *drm_dev_alloc(struct drm_driver *driver,
+struct drm_device *drm_dev_alloc(const struct drm_driver *driver,
 				 struct device *parent);
 int drm_dev_register(struct drm_device *dev, unsigned long flags);
 void drm_dev_unregister(struct drm_device *dev);