drm/vblank: Enable precise vblank timestamps for interlaced and doublescan modes.

Testing showed the current code can already handle doublescan
video modes just fine. A trivial tweak makes it work for interlaced
scanout as well.

Tested and shown to be precise on Radeon rv530, r600 and
Intel 945-GME.

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

1 files changed, 6 insertions, 8 deletions

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 22f3bf5ecbd..53120a72a48 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -493,6 +493,12 @@ void drm_calc_timestamping_constants(struct drm_crtc *crtc)
         /* Dot clock in Hz: */
         dotclock = (u64) crtc->hwmode.clock * 1000;
 
+        /* Fields of interlaced scanout modes are only halve a frame duration.
+         * Double the dotclock to get halve the frame-/line-/pixelduration.
+         */
+        if (crtc->hwmode.flags & DRM_MODE_FLAG_INTERLACE)
+                dotclock *= 2;
+
         /* Valid dotclock? */
         if (dotclock > 0) {
                 /* Convert scanline length in pixels and video dot clock to
@@ -605,14 +611,6 @@ int drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev, int crtc,
                 return -EAGAIN;
         }
 
-        /* Don't know yet how to handle interlaced or
-         * double scan modes. Just no-op for now.
-         */
-        if (mode->flags & (DRM_MODE_FLAG_INTERLACE | DRM_MODE_FLAG_DBLSCAN)) {
-                DRM_DEBUG("crtc %d: Noop due to unsupported mode.\n", crtc);
-                return -ENOTSUPP;
-        }
-
         /* Get current scanout position with system timestamp.
          * Repeat query up to DRM_TIMESTAMP_MAXRETRIES times
          * if single query takes longer than max_error nanoseconds.