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

include/drm/drm_mode_config.h

@@ -929,7 +929,23 @@ struct drm_mode_config {
 	const struct drm_mode_config_helper_funcs *helper_private;
 };
 
-void drm_mode_config_init(struct drm_device *dev);
+int __must_check drmm_mode_config_init(struct drm_device *dev);
+
+/**
+ * drm_mode_config_init - DRM mode_configuration structure initialization
+ * @dev: DRM device
+ *
+ * This is the unmanaged version of drmm_mode_config_init() for drivers which
+ * still explicitly call drm_mode_config_cleanup().
+ *
+ * FIXME: This function is deprecated and drivers should be converted over to
+ * drmm_mode_config_init().
+ */
+static inline int drm_mode_config_init(struct drm_device *dev)
+{
+	return drmm_mode_config_init(dev);
+}
+
 void drm_mode_config_reset(struct drm_device *dev);
 void drm_mode_config_cleanup(struct drm_device *dev);