drm/radeon: prefer lower reference dividers

BugLink: https://bugs.launchpad.net/bugs/1791312
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@gmail.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
(cherry picked from commit 2e26ccb119bde03584be53406bbd22e711b0d6e6)
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
index ddfe91efa61e4bef713454a8738429898df21053..4f94b78cb46472bba2d60116139bc2aeea0a8f2b 100644 (file)
--- a/drivers/gpu/drm/radeon/radeon_display.c
+++ b/drivers/gpu/drm/radeon/radeon_display.c
@@ -923,12 +923,12 @@ static void avivo_get_fb_ref_div(unsigned nom, unsigned den, unsigned post_div,
        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;
        }
 }