drm/i915: Fix scanoutpos calculations for interlaced modes

The scanline counter counts lines in the current field, not the entire
frame. But the crtc_ timings are the values for the entire frame. Divide
the vertical timings by 2 to make them match the scanline counter.

The rounding was carefully chosen to make it do the right thing wrt. the
observed scanline counter and ISR vblank bit behaviour.

Reviewed-by: mario.kleiner.de@gmail.com
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index b6e4a762806beb6e80958bdfb8b8022a789fbc64..eacbb2f9e09126699e8342c07be57adbd9ad960e 100644 (file)
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -698,6 +698,12 @@ static int i915_get_crtc_scanoutpos(struct drm_device *dev, int pipe,
        vbl_start = mode->crtc_vblank_start;
        vbl_end = mode->crtc_vblank_end;
 
+       if (mode->flags & DRM_MODE_FLAG_INTERLACE) {
+               vbl_start = DIV_ROUND_UP(vbl_start, 2);
+               vbl_end /= 2;
+               vtotal /= 2;
+       }
+
        ret |= DRM_SCANOUTPOS_VALID | DRM_SCANOUTPOS_ACCURATE;
 
        /*