[RFC PATCH v2 1/3] drm: add support modifiers for drivers whose planes only support linear layout

[Tomohito Esaki <etom@xxxxxxxxxx>]

The LINEAR modifier is advertised as default if a driver doesn't specify
modifiers. However, there are legacy drivers such as radeon that do not
support modifiers but infer the actual layout of the underlying buffer.
Therefore, a new flag not_support_fb_modifires is introduced for these
legacy drivers. Allow_fb_modifiers will be replaced with this new flag.

Signed-off-by: Tomohito Esaki <etom@xxxxxxxxxx>
---
 drivers/gpu/drm/drm_plane.c   | 15 ++++++++++++---
 include/drm/drm_mode_config.h | 10 ++++++++++
 include/drm/drm_plane.h       |  3 +++
 3 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_plane.c b/drivers/gpu/drm/drm_plane.c
index deeec60a3315..5aa7e241971e 100644
--- a/drivers/gpu/drm/drm_plane.c
+++ b/drivers/gpu/drm/drm_plane.c
@@ -237,6 +237,10 @@ static int __drm_universal_plane_init(struct drm_device *dev,
 				      const char *name, va_list ap)
 {
 	struct drm_mode_config *config = &dev->mode_config;
+	const uint64_t default_modifiers[] = {
+		DRM_FORMAT_MOD_LINEAR,
+		DRM_FORMAT_MOD_INVALID
+	};
 	unsigned int format_modifier_count = 0;
 	int ret;
 
@@ -277,6 +281,11 @@ static int __drm_universal_plane_init(struct drm_device *dev,
 
 		while (*temp_modifiers++ != DRM_FORMAT_MOD_INVALID)
 			format_modifier_count++;
+	} else {
+		if (!dev->mode_config.fb_modifiers_not_supported) {
+			format_modifiers = default_modifiers;
+			format_modifier_count = 1;
+		}
 	}
 
 	/* autoset the cap and check for consistency across all planes */
@@ -341,7 +350,7 @@ static int __drm_universal_plane_init(struct drm_device *dev,
 		drm_object_attach_property(&plane->base, config->prop_src_h, 0);
 	}
 
-	if (config->allow_fb_modifiers)
+	if (format_modifier_count)
 		create_in_format_blob(dev, plane);
 
 	return 0;
@@ -368,8 +377,8 @@ static int __drm_universal_plane_init(struct drm_device *dev,
  * drm_universal_plane_init() to let the DRM managed resource infrastructure
  * take care of cleanup and deallocation.
  *
- * Drivers supporting modifiers must set @format_modifiers on all their planes,
- * even those that only support DRM_FORMAT_MOD_LINEAR.
+ * For drivers supporting modifiers, all planes will advertise
+ * DRM_FORMAT_MOD_LINEAR support, if @format_modifiers is not set.
  *
  * Returns:
  * Zero on success, error code on failure.
diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
index 48b7de80daf5..c56f298c55bd 100644
--- a/include/drm/drm_mode_config.h
+++ b/include/drm/drm_mode_config.h
@@ -920,6 +920,16 @@ struct drm_mode_config {
 	 */
 	bool allow_fb_modifiers;
 
+	/**
+	 * @fb_modifiers_not_supported:
+	 *
+	 * This flag is for legacy drivers such as radeon that do not support
+	 * modifiers but infer the actual layout of the underlying buffer.
+	 * Generally, each drivers must support modifiers, this flag should not
+	 * be set.
+	 */
+	bool fb_modifiers_not_supported;
+
 	/**
 	 * @normalize_zpos:
 	 *
diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
index 0c1102dc4d88..cad641b1f797 100644
--- a/include/drm/drm_plane.h
+++ b/include/drm/drm_plane.h
@@ -803,6 +803,9 @@ void *__drmm_universal_plane_alloc(struct drm_device *dev,
  *
  * The @drm_plane_funcs.destroy hook must be NULL.
  *
+ * For drivers supporting modifiers, all planes will advertise
+ * DRM_FORMAT_MOD_LINEAR support, if @format_modifiers is not set.
+ *
  * Returns:
  * Pointer to new plane, or ERR_PTR on failure.
  */
-- 
2.25.1