From fc8c70526bd30733ea8667adb8b8ffebea30a8ed Mon Sep 17 00:00:00 2001
From: Kai-Heng Feng <kai.heng.feng@canonical.com>
Date: Wed, 26 Aug 2020 01:33:48 +0800
Subject: [PATCH] drm/radeon: Prefer lower feedback dividers
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Git-commit: fc8c70526bd30733ea8667adb8b8ffebea30a8ed
No-fix: 5150dd85bdfa08143cacf1b4249121651bed3c35
Patch-mainline: v5.9-rc4
References: git-fixes

Commit 2e26ccb119bd ("drm/radeon: prefer lower reference dividers")
fixed screen flicker for HP Compaq nx9420 but breaks other laptops like
Asus X50SL.

Turns out we also need to favor lower feedback dividers.

Users confirmed this change fixes the regression and doesn't regress the
original fix.

Fixes: 2e26ccb119bd ("drm/radeon: prefer lower reference dividers")
Buglink: https://bugs.launchpad.net/bugs/1791312
Buglink: https://bugs.launchpad.net/bugs/1861554
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/radeon/radeon_display.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
index e0ae911ef427..7b69d6dfe44a 100644
--- a/drivers/gpu/drm/radeon/radeon_display.c
+++ b/drivers/gpu/drm/radeon/radeon_display.c
@@ -933,7 +933,7 @@ static void avivo_get_fb_ref_div(unsigned nom, unsigned den, unsigned post_div,
 
 	/* get matching reference and feedback divider */
 	*ref_div = min(max(den/post_div, 1u), ref_div_max);
-	*fb_div = DIV_ROUND_CLOSEST(nom * *ref_div * post_div, den);
+	*fb_div = max(nom * *ref_div * post_div / den, 1u);
 
 	/* limit fb divider to its maximum */
 	if (*fb_div > fb_div_max) {
-- 
2.16.4