drm/encoder: Introduce drmm_encoder_init

The DRM-managed function to register an encoder is
drmm_encoder_alloc() and its variants, which will allocate the underlying
structure and initialisation the encoder.

However, we might want to separate the structure creation and the encoder
initialisation, for example if the structure is shared across multiple DRM
entities, for example an encoder and a connector.

Let's create an helper to only initialise an encoder that would be passed
as an argument.
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20220711173939.1132294-4-maxime@cerno.tech

drivers/gpu/drm/drm_encoder.c

@@ -27,6 +27,7 @@
 #include <drm/drm_drv.h>
 #include <drm/drm_encoder.h>
 #include <drm/drm_managed.h>
+#include <drm/drm_print.h>
 
 #include "drm_crtc_internal.h"
 
@@ -148,9 +149,9 @@ static int __drm_encoder_init(struct drm_device *dev,
  * the encoder structure. The encoder structure should not be allocated with
  * devm_kzalloc().
  *
- * Note: consider using drmm_encoder_alloc() instead of drm_encoder_init() to
- * let the DRM managed resource infrastructure take care of cleanup and
- * deallocation.
+ * Note: consider using drmm_encoder_alloc() or drmm_encoder_init()
+ * instead of drm_encoder_init() to let the DRM managed resource
+ * infrastructure take care of cleanup and deallocation.
  *
  * Returns:
  * Zero on success, error code on failure.
@@ -212,6 +213,30 @@ static void drmm_encoder_alloc_release(struct drm_device *dev, void *ptr)
 	drm_encoder_cleanup(encoder);
 }
 
+__printf(5, 0)
+static int __drmm_encoder_init(struct drm_device *dev,
+			       struct drm_encoder *encoder,
+			       const struct drm_encoder_funcs *funcs,
+			       int encoder_type,
+			       const char *name,
+			       va_list args)
+{
+	int ret;
+
+	if (drm_WARN_ON(dev, funcs && funcs->destroy))
+		return -EINVAL;
+
+	ret = __drm_encoder_init(dev, encoder, funcs, encoder_type, name, args);
+	if (ret)
+		return ret;
+
+	ret = drmm_add_action_or_reset(dev, drmm_encoder_alloc_release, encoder);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
 void *__drmm_encoder_alloc(struct drm_device *dev, size_t size, size_t offset,
 			   const struct drm_encoder_funcs *funcs,
 			   int encoder_type, const char *name, ...)
@@ -221,9 +246,6 @@ void *__drmm_encoder_alloc(struct drm_device *dev, size_t size, size_t offset,
 	va_list ap;
 	int ret;
 
-	if (WARN_ON(funcs && funcs->destroy))
-		return ERR_PTR(-EINVAL);
-
 	container = drmm_kzalloc(dev, size, GFP_KERNEL);
 	if (!container)
 		return ERR_PTR(-ENOMEM);
@@ -231,19 +253,50 @@ void *__drmm_encoder_alloc(struct drm_device *dev, size_t size, size_t offset,
 	encoder = container + offset;
 
 	va_start(ap, name);
-	ret = __drm_encoder_init(dev, encoder, funcs, encoder_type, name, ap);
+	ret = __drmm_encoder_init(dev, encoder, funcs, encoder_type, name, ap);
 	va_end(ap);
 	if (ret)
 		return ERR_PTR(ret);
 
-	ret = drmm_add_action_or_reset(dev, drmm_encoder_alloc_release, encoder);
-	if (ret)
-		return ERR_PTR(ret);
-
 	return container;
 }
 EXPORT_SYMBOL(__drmm_encoder_alloc);
 
+/**
+ * drmm_encoder_init - Initialize a preallocated encoder
+ * @dev: drm device
+ * @encoder: the encoder to init
+ * @funcs: callbacks for this encoder (optional)
+ * @encoder_type: user visible type of the encoder
+ * @name: printf style format string for the encoder name, or NULL for default name
+ *
+ * Initializes a preallocated encoder. Encoder should be subclassed as
+ * part of driver encoder objects. Cleanup is automatically handled
+ * through registering drm_encoder_cleanup() with drmm_add_action(). The
+ * encoder structure should be allocated with drmm_kzalloc().
+ *
+ * The @drm_encoder_funcs.destroy hook must be NULL.
+ *
+ * Returns:
+ * Zero on success, error code on failure.
+ */
+int drmm_encoder_init(struct drm_device *dev, struct drm_encoder *encoder,
+		      const struct drm_encoder_funcs *funcs,
+		      int encoder_type, const char *name, ...)
+{
+	va_list ap;
+	int ret;
+
+	va_start(ap, name);
+	ret = __drmm_encoder_init(dev, encoder, funcs, encoder_type, name, ap);
+	va_end(ap);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+EXPORT_SYMBOL(drmm_encoder_init);
+
 static struct drm_crtc *drm_encoder_get_crtc(struct drm_encoder *encoder)
 {
 	struct drm_connector *connector;

include/drm/drm_encoder.h

@@ -194,6 +194,12 @@ int drm_encoder_init(struct drm_device *dev,
 		     const struct drm_encoder_funcs *funcs,
 		     int encoder_type, const char *name, ...);
 
+__printf(5, 6)
+int drmm_encoder_init(struct drm_device *dev,
+		      struct drm_encoder *encoder,
+		      const struct drm_encoder_funcs *funcs,
+		      int encoder_type, const char *name, ...);
+
 __printf(6, 7)
 void *__drmm_encoder_alloc(struct drm_device *dev,
 			   size_t size, size_t offset,