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 <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Reviewed-by: Laurent Pinchart <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_plane.c

···
 				      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;
 
···
 
 		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,
···
 		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;
···
  * 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

···
  *
  * 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.
  */