drm: Simplify the math in drm_calc_timestamping_constants()

drm_calc_timestamping_constants() makes the math more complex
than necessary.
- multipying the dotclock by 1000 is pointless, just makes all the
  numbers bigger
- div64_u64() is also pointless, div_u64 is enough
- pixeldur_ns doesn't need any 64bit math

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

1 files changed, 11 insertions, 15 deletions

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 03f6a149b887..3283669a9083 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -451,10 +451,7 @@ void drm_calc_timestamping_constants(struct drm_crtc *crtc,
                                      const struct drm_display_mode *mode)
 {
         s64 linedur_ns = 0, pixeldur_ns = 0, framedur_ns = 0;
-        u64 dotclock;
-
-        /* Dot clock in Hz: */
-        dotclock = (u64) mode->clock * 1000;
+        int dotclock = mode->clock;
 
         /* Fields of interlaced scanout modes are only half a frame duration.
          * Double the dotclock to get half the frame-/line-/pixelduration.
@@ -464,17 +461,16 @@ void drm_calc_timestamping_constants(struct drm_crtc *crtc,
 
         /* Valid dotclock? */
         if (dotclock > 0) {
-                int frame_size;
-                /* Convert scanline length in pixels and video dot clock to
-                 * line duration, frame duration and pixel duration in
-                 * nanoseconds:
+                int frame_size = mode->crtc_htotal * mode->crtc_vtotal;
+
+                /*
+                 * Convert scanline length in pixels and video
+                 * dot clock to line duration, frame duration
+                 * and pixel duration in nanoseconds:
                  */
-                pixeldur_ns = (s64) div64_u64(1000000000, dotclock);
-                linedur_ns  = (s64) div64_u64(((u64) mode->crtc_htotal *
-                                              1000000000), dotclock);
-                frame_size = mode->crtc_htotal * mode->crtc_vtotal;
-                framedur_ns = (s64) div64_u64((u64) frame_size * 1000000000,
-                                              dotclock);
+                pixeldur_ns = 1000000 / dotclock;
+                linedur_ns  = div_u64((u64) mode->crtc_htotal * 1000000, dotclock);
+                framedur_ns = div_u64((u64) frame_size * 1000000, dotclock);
         } else
                 DRM_ERROR("crtc %d: Can't calculate constants, dotclock = 0!\n",
                           crtc->base.id);
@@ -487,7 +483,7 @@ void drm_calc_timestamping_constants(struct drm_crtc *crtc,
                   crtc->base.id, mode->crtc_htotal,
                   mode->crtc_vtotal, mode->crtc_vdisplay);
         DRM_DEBUG("crtc %d: clock %d kHz framedur %d linedur %d, pixeldur %d\n",
-                  crtc->base.id, (int) dotclock/1000, (int) framedur_ns,
+                  crtc->base.id, dotclock, (int) framedur_ns,
                   (int) linedur_ns, (int) pixeldur_ns);
 }
 EXPORT_SYMBOL(drm_calc_timestamping_constants);