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Commit 85a7ce67 authored by Daniel Kurtz's avatar Daniel Kurtz Committed by Dave Airlie
Browse files

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: default avatarDaniel Kurtz <djkurtz@chromium.org>
Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
parent dd66cc2e

drivers/gpu/drm/drm_irq.c

+5 −1
Original line number Diff line number Diff line
@@ -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);