diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c index 20432762d30f..cfa4d369c98c 100644 --- a/drivers/gpu/drm/i915/i915_irq.c +++ b/drivers/gpu/drm/i915/i915_irq.c @@ -914,6 +914,18 @@ static int i915_get_crtc_scanoutpos(struct drm_device *dev, int pipe, vbl_end *= htotal; vtotal *= htotal; + /* + * In interlaced modes, the pixel counter counts all pixels, + * so one field will have htotal more pixels. In order to avoid + * the reported position from jumping backwards when the pixel + * counter is beyond the length of the shorter field, just + * clamp the position the length of the shorter field. This + * matches how the scanline counter based position works since + * the scanline counter doesn't count the two half lines. + */ + if (position >= vtotal) + position = vtotal - 1; + /* * Start of vblank interrupt is triggered at start of hsync, * just prior to the first active line of vblank. However we