drm/radeon: fix deferred page-flip detection logic on Avivo-based ASICs

This fixes page-flip-related flickering observed on Iconia Tab W500.

The update_pending status returned by radeon_page_flip is very accurate on
Avivo-based ASICs when vpos is negative.

Experiments were conducted on several ASIC generations ranging from RS690
to Cayman where the page flip was artificially timed to occur at a specific
vpos. With negative vpos, overriding update_pending always lead to
flickering.

The same experiment on RV380 and RV410 showed that update_pending is not
accurate with negative vpos. In most cases update_pending == 1 is returned
although the flip would complete before the start of the next frame.
Therefore I left the behaviour unchanged for pre-AVIVO ASICs for
performance reasons, although this may result in flickering in rare cases.

This change also makes the logic a little easier to understand.

Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Mario Kleiner <mario.kleiner@tuebingen.mpg.de>
Signed-off-by: Dave Airlie <airlied@redhat.com>

diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
index 7cb062daa71ea1d6352226d7cbf213fee0f2ea13..1f98e5fbc7333b888de5a3dedc865ba1321f426b 100644 (file)
--- a/drivers/gpu/drm/radeon/radeon_display.c
+++ b/drivers/gpu/drm/radeon/radeon_display.c
@@ -303,8 +303,17 @@ void radeon_crtc_handle_flip(struct radeon_device *rdev, int crtc_id)
        if (update_pending &&
            (DRM_SCANOUTPOS_VALID & radeon_get_crtc_scanoutpos(rdev->ddev, crtc_id,
                                                               &vpos, &hpos)) &&
-           (vpos >=0) &&
-           (vpos < (99 * rdev->mode_info.crtcs[crtc_id]->base.hwmode.crtc_vdisplay)/100)) {
+           ((vpos >= (99 * rdev->mode_info.crtcs[crtc_id]->base.hwmode.crtc_vdisplay)/100) ||
+            (vpos < 0 && !ASIC_IS_AVIVO(rdev)))) {
+               /* crtc didn't flip in this target vblank interval,
+                * but flip is pending in crtc. Based on the current
+                * scanout position we know that the current frame is
+                * (nearly) complete and the flip will (likely)
+                * complete before the start of the next frame.
+                */
+               update_pending = 0;
+       }
+       if (update_pending) {
                /* crtc didn't flip in this target vblank interval,
                 * but flip is pending in crtc. It will complete it
                 * in next vblank interval, so complete the flip at