drm: add support modifiers for drivers whose planes only support linear layout

The LINEAR modifier is advertised as default if a driver doesn't specify
modifiers.

v2:
 - rebase to the latest master branch (5.16.0+)
    + "drm/plane: Make format_mod_supported truly optional" patch [1]
   [1] https://patchwork.freedesktop.org/patch/467940/?series=98255&rev=3

v3:
 - change the order as follows:
   1. add fb_modifiers_not_supported flag
   2. add default modifiers
   3. remove allow_fb_modifiers flag

v5:
 - change default_modifiers array from non-static to static
 - remove terminator in default_modifiers array
 - use ARRAY_SIZE to get the format_modifier_count
 - update sanity check in plane init func to use the
   fb_modifiers_not_supported
 - modify kernel docs

Signed-off-by: Tomohito Esaki <etom@igel.co.jp>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220128060836.11216-3-etom@igel.co.jp

drivers/gpu/drm/drm_plane.c

@@ -237,6 +237,9 @@ static int __drm_universal_plane_init(struct drm_device *dev,
 				      const char *name, va_list ap)
 {
 	struct drm_mode_config *config = &dev->mode_config;
+	static const uint64_t default_modifiers[] = {
+		DRM_FORMAT_MOD_LINEAR,
+	};
 	unsigned int format_modifier_count = 0;
 	int ret;
 
@@ -277,16 +280,16 @@ 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 = ARRAY_SIZE(default_modifiers);
+		}
 	}
 
 	/* autoset the cap and check for consistency across all planes */
-	if (format_modifier_count) {
-		drm_WARN_ON(dev, !config->allow_fb_modifiers &&
-			    !list_empty(&config->plane_list));
-		config->allow_fb_modifiers = true;
-	} else {
-		drm_WARN_ON(dev, config->allow_fb_modifiers);
-	}
+	drm_WARN_ON(dev, config->fb_modifiers_not_supported &&
+				format_modifier_count);
 
 	plane->modifier_count = format_modifier_count;
 	plane->modifiers = kmalloc_array(format_modifier_count,
@@ -341,7 +344,7 @@ 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 +371,8 @@ 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.
+ * Drivers that only support the DRM_FORMAT_MOD_LINEAR modifier support may set
+ * @format_modifiers to NULL. The plane will advertise the linear modifier.
  *
  * Returns:
  * Zero on success, error code on failure.

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.
  *
+ * Drivers that only support the DRM_FORMAT_MOD_LINEAR modifier support may set
+ * @format_modifiers to NULL. The plane will advertise the linear modifier.
+ *
  * Returns:
  * Pointer to new plane, or ERR_PTR on failure.
  */