drm/radeon: improve PLL params if we don't match exactly v2

Otherwise we might be quite off on older chipsets.

v2: keep ref_div minimum

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

1 files changed, 7 insertions, 6 deletions

diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
index 2f42912031ac..063d4255137f 100644
--- a/drivers/gpu/drm/radeon/radeon_display.c
+++ b/drivers/gpu/drm/radeon/radeon_display.c
@@ -865,7 +865,7 @@ void radeon_compute_pll_avivo(struct radeon_pll *pll,
         unsigned post_div_min, post_div_max, post_div;
         unsigned ref_div_min, ref_div_max, ref_div;
         unsigned post_div_best, diff_best;
-        unsigned nom, den, tmp;
+        unsigned nom, den;
 
         /* determine allowed feedback divider range */
         fb_div_min = pll->min_feedback_div;
@@ -941,22 +941,23 @@ void radeon_compute_pll_avivo(struct radeon_pll *pll,
         ref_div_max = min(210 / post_div, ref_div_max);
 
         /* get matching reference and feedback divider */
-        ref_div = max(den / post_div, 1u);
-        fb_div = nom;
+        ref_div = max(DIV_ROUND_CLOSEST(den, post_div), 1u);
+        fb_div = DIV_ROUND_CLOSEST(nom * ref_div * post_div, den);
 
         /* we're almost done, but reference and feedback
            divider might be to large now */
 
-        tmp = ref_div;
+        nom = fb_div;
+        den = ref_div;
 
         if (fb_div > fb_div_max) {
-                ref_div = ref_div * fb_div_max / fb_div;
+                ref_div = DIV_ROUND_CLOSEST(den * fb_div_max, nom);
                 fb_div = fb_div_max;
         }
 
         if (ref_div > ref_div_max) {
                 ref_div = ref_div_max;
-                fb_div = nom * ref_div_max / tmp;
+                fb_div = DIV_ROUND_CLOSEST(nom * ref_div_max, den);
         }
 
         /* reduce the numbers to a simpler ratio once more */