For a kms driver to support immediate disable of vblank irq's reliably without introducing off by one errors or other mayhem for clients, it must not only support a hardware vblank counter query, but also high precision vblank timestamping, so vblank count and timestamp can be instantaneously reinitialzed to valid values. Additionally the exposed hardware counter must behave as if it is incrementing at leading edge of vblank to avoid off by one errors during reinitialization of the counter while the display happens to be inside or close to vblank.
Check during drm_vblank_init that a driver which claims to be capable of vblank_disable_immediate at least supports high precision timestamping and prevent use of instant disable if that isn't present as a minimum requirement.
Signed-off-by: Mario Kleiner mario.kleiner.de@gmail.com Cc: Ville Syrjälä ville.syrjala@linux.intel.com Cc: Michel Dänzer michel@daenzer.net Cc: Thierry Reding treding@nvidia.com Cc: Dave Airlie airlied@redhat.com --- drivers/gpu/drm/drm_irq.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index af9662e..6efe822 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -336,6 +336,12 @@ int drm_vblank_init(struct drm_device *dev, int num_crtcs) else DRM_INFO("No driver support for vblank timestamp query.\n");
+ /* Must have precise timestamping for reliable vblank instant disable */ + if (dev->vblank_disable_immediate && !dev->driver->get_vblank_timestamp) { + dev->vblank_disable_immediate = false; + DRM_ERROR("Set vblank_disable_immediate, but not supported.\n"); + } + dev->vblank_disable_allowed = false;
return 0;