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>

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 22f3bf5..53120a7 100644 (file)
--- 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.