Weston internals and Wayland clients assume that output presentation
clock cannot go backwards. Therefore require unconditionally that KMS
uses the monotonic clock.
The kernel unconditionally supports DRM_CAP_TIMESTAMP_MONOTONIC. See:
commit 25e1a79874eb3821d93310c908cc0a81b47af060
Author: Arnd Bergmann <arnd@arndb.de>
Date: Wed Oct 11 17:20:13 2017 +0200
drm: vblank: remove drm_timestamp_monotonic parameter
That one removed the final possibility of DRM_CAP_TIMESTAMP_MONOTONIC
being false, by removing the module option. But even before that, all
drivers have been supporting monotonic, since
commit c61eef726a78ae77b6ce223d01ea2130f465fe5c
Author: Imre Deak <imre.deak@intel.com>
Date: Tue Oct 23 18:53:26 2012 +0000
drm: add support for monotonic vblank timestamps
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
f48277b577