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Subject[PATCH] drm: make frame duration time calculation more precise
Date
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>
---
drivers/gpu/drm/drm_irq.c | 6 +++++-
1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 19c01ca..05c91e0 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -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);
--
1.7.7.3


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