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drm: make frame duration time calculation more precise

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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>
This commit is contained in:
Daniel Kurtz 2012-12-27 01:01:46 +00:00 committed by Dave Airlie
parent dd66cc2e1f
commit 85a7ce67f3
1 changed files with 5 additions and 1 deletions
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6
drivers/gpu/drm/drm_irq.c
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@ -505,6 +505,7 @@ 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:
@ -512,7 +513,10 @@ void drm_calc_timestamping_constants(struct drm_crtc *crtc)
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);