linux-kernel - [PATCH 3.16 092/132] drm/radeon: prefer lower reference dividers

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Message-ID: <lsq.1568989415.591577538@decadent.org.uk>
Date:   Fri, 20 Sep 2019 15:23:35 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Paul Dufresne" <dufresnep@...il.com>,
        "Christian König" <christian.koenig@....com>,
        "Alex Deucher" <alexander.deucher@....com>
Subject: [PATCH 3.16 092/132] drm/radeon: prefer lower reference dividers

3.16.74-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Christian König <christian.koenig@....com>

commit 2e26ccb119bde03584be53406bbd22e711b0d6e6 upstream.

Instead of the closest reference divider prefer the lowest,
this fixes flickering issues on HP Compaq nx9420.

Bugs: https://bugs.freedesktop.org/show_bug.cgi?id=108514
Suggested-by: Paul Dufresne <dufresnep@...il.com>
Signed-off-by: Christian König <christian.koenig@....com>
Acked-by: Alex Deucher <alexander.deucher@....com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/gpu/drm/radeon/radeon_display.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/radeon/radeon_display.c
+++ b/drivers/gpu/drm/radeon/radeon_display.c
@@ -942,12 +942,12 @@ static void avivo_get_fb_ref_div(unsigne
 	ref_div_max = max(min(100 / post_div, ref_div_max), 1u);
 
 	/* get matching reference and feedback divider */
-	*ref_div = min(max(DIV_ROUND_CLOSEST(den, post_div), 1u), ref_div_max);
+	*ref_div = min(max(den/post_div, 1u), ref_div_max);
 	*fb_div = DIV_ROUND_CLOSEST(nom * *ref_div * post_div, den);
 
 	/* limit fb divider to its maximum */
         if (*fb_div > fb_div_max) {
-		*ref_div = DIV_ROUND_CLOSEST(*ref_div * fb_div_max, *fb_div);
+		*ref_div = (*ref_div * fb_div_max)/(*fb_div);
 		*fb_div = fb_div_max;
 	}
 }