drm: make frame duration time calculation more precise
It is a bit more precise to compute the total number of pixels first and
then divide, rather than multiplying the line pixel count by the
already-rounded line duration.
Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
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 71f8205..38e7992 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -505,6 +505,7 @@
/* 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:
@@ -512,7 +513,10 @@
pixeldur_ns = (s64) div64_u64(1000000000, dotclock);
linedur_ns = (s64) div64_u64(((u64) crtc->hwmode.crtc_htotal *
1000000000), dotclock);
- framedur_ns = (s64) crtc->hwmode.crtc_vtotal * linedur_ns;
+ frame_size = crtc->hwmode.crtc_htotal *
+ crtc->hwmode.crtc_vtotal;
+ framedur_ns = (s64) div64_u64((u64) frame_size * 1000000000,
+ dotclock);
} else
DRM_ERROR("crtc %d: Can't calculate constants, dotclock = 0!\n",
crtc->base.id);