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

Documentation/gpu/drm-kms.rst

@@ -3,7 +3,7 @@ Kernel Mode Setting (KMS)
 =========================
 
 Drivers must initialize the mode setting core by calling
-drm_mode_config_init() on the DRM device. The function
+drmm_mode_config_init() on the DRM device. The function
 initializes the :c:type:`struct drm_device <drm_device>`
 mode_config field and never fails. Once done, mode configuration must
 be setup by initializing the following fields.

drivers/gpu/drm/drm_drv.c

@@ -98,6 +98,8 @@ static void drm_minor_alloc_release(struct drm_device *dev, void *data)
 	struct drm_minor *minor = data;
 	unsigned long flags;
 
+	WARN_ON(dev != minor->dev);
+
 	put_device(minor->kdev);
 
 	spin_lock_irqsave(&drm_minor_lock, flags);
@@ -266,8 +268,7 @@ void drm_minor_release(struct drm_minor *minor)
  *
  * The following example shows a typical structure of a DRM display driver.
  * The example focus on the probe() function and the other functions that is
- * almost always present and serves as a demonstration of devm_drm_dev_init()
+ * almost always present and serves as a demonstration of devm_drm_dev_init().
- * usage with its accompanying drm_driver->release callback.
  *
  * .. code-block:: c
  *
@@ -277,16 +278,8 @@ void drm_minor_release(struct drm_minor *minor)
  *		struct clk *pclk;
  *	};
  *
- *	static void driver_drm_release(struct drm_device *drm)
- *	{
- *		struct driver_device *priv = container_of(...);
- *
- *		drm_mode_config_cleanup(drm);
- *	}
- *
  *	static struct drm_driver driver_drm_driver = {
  *		[...]
- *		.release = driver_drm_release,
  *	};
  *
  *	static int driver_probe(struct platform_device *pdev)
@@ -311,7 +304,9 @@ void drm_minor_release(struct drm_minor *minor)
  *		}
  *		drmm_add_final_kfree(drm, priv);
  *
- *		drm_mode_config_init(drm);
+ *		ret = drmm_mode_config_init(drm);
+ *		if (ret)
+ *			return ret;
  *
  *		priv->userspace_facing = drmm_kzalloc(..., GFP_KERNEL);
  *		if (!priv->userspace_facing)
@@ -709,8 +704,7 @@ static void devm_drm_dev_init_release(void *data)
  * @driver: DRM driver
  *
  * Managed drm_dev_init(). The DRM device initialized with this function is
- * automatically put on driver detach using drm_dev_put(). You must supply a
+ * automatically put on driver detach using drm_dev_put().
- * &drm_driver.release callback to control the finalization explicitly.
  *
  * RETURNS:
  * 0 on success, or error code on failure.
@@ -721,9 +715,6 @@ int devm_drm_dev_init(struct device *parent,
 {
 	int ret;
 
-	if (WARN_ON(!driver->release))
-		return -EINVAL;
-
 	ret = drm_dev_init(dev, driver, parent);
 	if (ret)
 		return ret;

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)
 {

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);