drm/i915: Make sure vsyncshift is positive

If vsyncshift comes out as negative, add one htotal to it to get the
corresponding positive value.

This is rather theoretical as it would require a mode where the
hsync+back porch is very long and the active+front porch very short.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index a0f4ac187f1a..56018b79da62 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -5369,7 +5369,8 @@ static void intel_set_pipe_timings(struct intel_crtc *intel_crtc)
         enum transcoder cpu_transcoder = intel_crtc->config.cpu_transcoder;
         struct drm_display_mode *adjusted_mode =
                 &intel_crtc->config.adjusted_mode;
-        uint32_t vsyncshift = 0, crtc_vtotal, crtc_vblank_end;
+        uint32_t crtc_vtotal, crtc_vblank_end;
+        int vsyncshift = 0;
 
         /* We need to be careful not to changed the adjusted mode, for otherwise
          * the hw state checker will get angry at the mismatch. */
@@ -5386,6 +5387,8 @@ static void intel_set_pipe_timings(struct intel_crtc *intel_crtc)
                 else
                         vsyncshift = adjusted_mode->crtc_hsync_start -
                                 adjusted_mode->crtc_htotal / 2;
+                if (vsyncshift < 0)
+                        vsyncshift += adjusted_mode->crtc_htotal;
         }
 
         if (INTEL_INFO(dev)->gen > 3)