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>

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 */