drm: Manage drm_mode_config_init with drmm_

drm_mode_config_cleanup is idempotent, so no harm in calling this
twice. This allows us to gradually switch drivers over by removing
explicit drm_mode_config_cleanup calls.

With this step it's now also possible that (at least for simple
drivers) automatic resource cleanup can be done correctly without a
drm_driver->release hook. Therefore allow this now in
devm_drm_dev_init().

Also with drmm_ explicit drm_driver->release hooks are kinda not the
best option: Drivers can always just register their current release
hook with drmm_add_action, but even better they could split them up to
simplify the unwinding for the driver load failure case. So deprecate
that hook to discourage future users.

v2: Fixup the example in the kerneldoc too.

v3:
- For paranoia, double check that minor->dev == dev in the release
  hook, because I botched the pointer math in the drmm library.
- Call drm_mode_config_cleanup when drmm_add_action fails, we'd be
  missing some mutex_destroy and ida_cleanup otherwise (Laurent)

v4: Add a drmm_add_action_or_reset (like devm_ has) to encapsulate this
pattern (Noralf).

v5: Fix oversight in the new drmm_add_action_or_reset macro (Noralf)

v4: Review from Sam:
- drmm_mode_config_init wrapper (also suggested by Thomas)
- improve commit message, explain better why ->relase is deprecated

v5:
- Make drmm_ the main function, with the old one as compat wrapper
  (Sam)
- Add FIXME comments to drm_mode_config_cleanup/init() that drivers
  shouldn't use these anymore.
- Move drmm_add_action_or_reset helper to an earlier patch.

Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: "Noralf Trønnes" <noralf@tronnes.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200323144950.3018436-27-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_mode_config.c

@@ -25,6 +25,7 @@
 #include <drm/drm_drv.h>
 #include <drm/drm_encoder.h>
 #include <drm/drm_file.h>
+#include <drm/drm_managed.h>
 #include <drm/drm_mode_config.h>
 #include <drm/drm_print.h>
 #include <linux/dma-resv.h>
@@ -373,8 +374,14 @@ static int drm_mode_create_standard_properties(struct drm_device *dev)
 	return 0;
 }
 
+static void drm_mode_config_init_release(struct drm_device *dev, void *ptr)
+{
+	drm_mode_config_cleanup(dev);
+}
+
 /**
- * drm_mode_config_init - initialize DRM mode_configuration structure
+ * drmm_mode_config_init - managed DRM mode_configuration structure
+ * 	initialization
  * @dev: DRM device
  *
  * Initialize @dev's mode_config structure, used for tracking the graphics
@@ -384,8 +391,12 @@ static int drm_mode_create_standard_properties(struct drm_device *dev)
  * problem, since this should happen single threaded at init time. It is the
  * driver's problem to ensure this guarantee.
  *
+ * Cleanup is automatically handled through registering drm_mode_config_cleanup
+ * with drmm_add_action().
+ *
+ * Returns: 0 on success, negative error value on failure.
  */
-void drm_mode_config_init(struct drm_device *dev)
+int drmm_mode_config_init(struct drm_device *dev)
 {
 	mutex_init(&dev->mode_config.mutex);
 	drm_modeset_lock_init(&dev->mode_config.connection_mutex);
@@ -443,8 +454,11 @@ void drm_mode_config_init(struct drm_device *dev)
 		drm_modeset_acquire_fini(&modeset_ctx);
 		dma_resv_fini(&resv);
 	}
+
+	return drmm_add_action_or_reset(dev, drm_mode_config_init_release,
+					NULL);
 }
-EXPORT_SYMBOL(drm_mode_config_init);
+EXPORT_SYMBOL(drmm_mode_config_init);
 
 /**
  * drm_mode_config_cleanup - free up DRM mode_config info
@@ -456,6 +470,9 @@ EXPORT_SYMBOL(drm_mode_config_init);
  * Note that since this /should/ happen single-threaded at driver/device
  * teardown time, no locking is required. It's the driver's job to ensure that
  * this guarantee actually holds true.
+ *
+ * FIXME: With the managed drmm_mode_config_init() it is no longer necessary for
+ * drivers to explicitly call this function.
  */
 void drm_mode_config_cleanup(struct drm_device *dev)
 {