[PATCH] drm: make frame duration time calculation more precise

[Daniel Kurtz]

On Wed, Dec 26, 2012 at 5:01 PM, Daniel Kurtz <djkurtz at chromium.org> wrote:

> 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 at chromium.org>
>

Ping?


> ---
>  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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