[PATCH 5.1 58/70] drm/radeon: prefer lower reference dividers

From: Greg Kroah-Hartman
Date: Sun Jun 09 2019 - 12:50:43 EST


From: Christian KÃnig <christian.koenig@xxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Christian KÃnig <christian.koenig@xxxxxxx>
Acked-by: Alex Deucher <alexander.deucher@xxxxxxx>
Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
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
@@ -922,12 +922,12 @@ 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;
}
}