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drm: Make drm_mode_vrefresh() a bit more accurate 

Do the refresh rate calculation with a single division. This gives
us slightly more accurate results, especially for interlaced since
we don't just double the final truncated result.

We do lose one bit compared to the old way, so with an interlaced
mode the new code can only handle ~2GHz instead of the ~4GHz the
old code handeled.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180313150759.27620-2-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
This commit is contained in:
Ville Syrjälä 2018-03-13 17:07:58 +02:00
parent df550548c6
commit 2f0e9d8049
1 changed files with 9 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
drivers/gpu/drm/drm_modes.c
View File

@ -773,24 +773,23 @@ EXPORT_SYMBOL(drm_mode_hsync);
int drm_mode_vrefresh(const struct drm_display_mode *mode)
{
int refresh = 0;
unsigned int calc_val;
if (mode->vrefresh > 0)
refresh = mode->vrefresh;
else if (mode->htotal > 0 && mode->vtotal > 0) {
int vtotal;
vtotal = mode->vtotal;
/* work out vrefresh the value will be x1000 */
calc_val = (mode->clock * 1000);
calc_val /= mode->htotal;
refresh = (calc_val + vtotal / 2) / vtotal;
unsigned int num, den;
num = mode->clock * 1000;
den = mode->htotal * mode->vtotal;
if (mode->flags & DRM_MODE_FLAG_INTERLACE)
refresh *= 2;
num *= 2;
if (mode->flags & DRM_MODE_FLAG_DBLSCAN)
refresh /= 2;
den *= 2;
if (mode->vscan > 1)
refresh /= mode->vscan;
den *= mode->vscan;
refresh = DIV_ROUND_CLOSEST(num, den);
}
return refresh;
}