drm: Add devm_drm_dev_alloc macro

Add a new macro helper to combine the usual init sequence in drivers,
consisting of a kzalloc + devm_drm_dev_init + drmm_add_final_kfree
triplet. This allows us to remove the rather unsightly
drmm_add_final_kfree from all currently merged drivers.

The kerneldoc is only added for this new function. Existing kerneldoc
and examples will be udated at the very end, since once all drivers
are converted over to devm_drm_dev_alloc we can unexport a lot of
interim functions and make the documentation for driver authors a lot
cleaner and less confusing. There will be only one true way to
initialize a drm_device at the end of this, which is going to be
devm_drm_dev_alloc.

v2:
- Actually explain what this is for in the commit message (Sam)
- Fix checkpatch issues (Sam)

Acked-by: Noralf Trønnes <noralf@tronnes.org>
Cc: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200415074034.175360-2-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_drv.c

@@ -739,6 +739,29 @@ int devm_drm_dev_init(struct device *parent,
 }
 EXPORT_SYMBOL(devm_drm_dev_init);
 
+void *__devm_drm_dev_alloc(struct device *parent, struct drm_driver *driver,
+			   size_t size, size_t offset)
+{
+	void *container;
+	struct drm_device *drm;
+	int ret;
+
+	container = kzalloc(size, GFP_KERNEL);
+	if (!container)
+		return ERR_PTR(-ENOMEM);
+
+	drm = container + offset;
+	ret = devm_drm_dev_init(parent, drm, driver);
+	if (ret) {
+		kfree(container);
+		return ERR_PTR(ret);
+	}
+	drmm_add_final_kfree(drm, container);
+
+	return container;
+}
+EXPORT_SYMBOL(__devm_drm_dev_alloc);
+
 /**
  * drm_dev_alloc - Allocate new DRM device
  * @driver: DRM driver to allocate device for

include/drm/drm_drv.h

@@ -623,6 +623,39 @@ int devm_drm_dev_init(struct device *parent,
 		      struct drm_device *dev,
 		      struct drm_driver *driver);
 
+void *__devm_drm_dev_alloc(struct device *parent, struct drm_driver *driver,
+			   size_t size, size_t offset);
+
+/**
+ * devm_drm_dev_alloc - Resource managed allocation of a &drm_device instance
+ * @parent: Parent device object
+ * @driver: DRM driver
+ * @type: the type of the struct which contains struct &drm_device
+ * @member: the name of the &drm_device within @type.
+ *
+ * This allocates and initialize a new DRM device. No device registration is done.
+ * Call drm_dev_register() to advertice the device to user space and register it
+ * with other core subsystems. This should be done last in the device
+ * initialization sequence to make sure userspace can't access an inconsistent
+ * state.
+ *
+ * The initial ref-count of the object is 1. Use drm_dev_get() and
+ * drm_dev_put() to take and drop further ref-counts.
+ *
+ * It is recommended that drivers embed &struct drm_device into their own device
+ * structure.
+ *
+ * Note that this manages the lifetime of the resulting &drm_device
+ * automatically using devres. The DRM device initialized with this function is
+ * automatically put on driver detach using drm_dev_put().
+ *
+ * RETURNS:
+ * Pointer to new DRM device, or ERR_PTR on failure.
+ */
+#define devm_drm_dev_alloc(parent, driver, type, member) \
+	((type *) __devm_drm_dev_alloc(parent, driver, sizeof(type), \
+				       offsetof(type, member)))
+
 struct drm_device *drm_dev_alloc(struct drm_driver *driver,
 				 struct device *parent);
 int drm_dev_register(struct drm_device *dev, unsigned long flags);