drm/radeon: avoid high jitter with small frac divs

Signed-off-by: Christian König <christian.koenig@amd.com>

1 files changed, 12 insertions, 2 deletions

diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
index 14bd701e316c..9ff0e2f1be6a 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;