[PATCH] drm/radeon: avoid high jitter with small frac divs

[Christian König]

From: Christian K?nig <christian.koe...@amd.com>

Signed-off-by: Christian K?nig <christian.koenig at amd.com>
---
 drivers/gpu/drm/radeon/radeon_display.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/radeon/radeon_display.c 
b/drivers/gpu/drm/radeon/radeon_display.c
index 14bd701..9ff0e2f 100644
--- a/drivers/gpu/drm/radeon/radeon_display.c
+++ b/drivers/gpu/drm/radeon/radeon_display.c
@@ -830,14 +830,14 @@ static void avivo_reduce_ratio(unsigned *nom, unsigned 
*den,

        /* make sure nominator is large enough */
         if (*nom < nom_min) {
-               tmp = (nom_min + *nom - 1) / *nom;
+               tmp = DIV_ROUND_UP(nom_min, *nom);
                *nom *= tmp;
                *den *= tmp;
        }

        /* make sure the denominator is large enough */
        if (*den < den_min) {
-               tmp = (den_min + *den - 1) / *den;
+               tmp = DIV_ROUND_UP(den_min, *den);
                *nom *= tmp;
                *den *= tmp;
        }
@@ -997,6 +997,16 @@ void radeon_compute_pll_avivo(struct radeon_pll *pll,
        /* this also makes sure that the reference divider is large enough */
        avivo_reduce_ratio(&fb_div, &ref_div, fb_div_min, ref_div_min);

+       /* avoid high jitter with small fractional dividers */
+       if (pll->flags & RADEON_PLL_USE_FRAC_FB_DIV && (fb_div % 10)) {
+               fb_div_min = max(fb_div_min, (9 - (fb_div % 10)) * 20 + 60);
+               if (fb_div < fb_div_min) {
+                       unsigned tmp = DIV_ROUND_UP(fb_div_min, fb_div);
+                       fb_div *= tmp;
+                       ref_div *= tmp;
+               }
+       }
+
        /* and finally save the result */
        if (pll->flags & RADEON_PLL_USE_FRAC_FB_DIV) {
                *fb_div_p = fb_div / 10;
-- 
1.9.1