[mutter] crtc/kms: Document meta_crtc_kms_get_modifiers

[Jonas Ådahl <jadahl src gnome org>]

commit 7f2dbb6c4449c0bd999ff1bdc37614f950b03aff
Author: Pekka Paalanen <pekka paalanen collabora com>
Date:   Wed Nov 21 15:12:32 2018 +0200

    crtc/kms: Document meta_crtc_kms_get_modifiers
    
    It has some details that may not be obvious from the function signature.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/341

 src/backends/native/meta-crtc-kms.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
---
diff --git a/src/backends/native/meta-crtc-kms.c b/src/backends/native/meta-crtc-kms.c
index f4962bece..b11d2d6b6 100644
--- a/src/backends/native/meta-crtc-kms.c
+++ b/src/backends/native/meta-crtc-kms.c
@@ -179,6 +179,20 @@ find_property_index (MetaGpu                    *gpu,
   return -1;
 }
 
+/**
+ * meta_crtc_kms_get_modifiers:
+ * @crtc: a #MetaCrtc object that has to be a #MetaCrtcKms
+ * @format: a DRM pixel format
+ *
+ * Returns a pointer to a #GArray containing all the supported
+ * modifiers for the given DRM pixel format on the CRTC's primary
+ * plane. The array element type is uint64_t.
+ *
+ * The caller must not modify or destroy the array or its contents.
+ *
+ * Returns NULL if the modifiers are not known or the format is not
+ * supported.
+ */
 GArray *
 meta_crtc_kms_get_modifiers (MetaCrtc *crtc,
                              uint32_t  format)