This is a note to let you know that I've just added the patch titled
drm/radeon: Prefer lower feedback dividers
to the 5.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-radeon-prefer-lower-feedback-dividers.patch
and it can be found in the queue-5.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 3fa04dfbb55a95e7c6075d0644f64bcb6e7f4ef8
Author: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
Date: Wed Aug 26 01:33:48 2020 +0800
drm/radeon: Prefer lower feedback dividers
[ Upstream commit 5150dd85bdfa08143cacf1b4249121651bed3c35 ]
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@xxxxxxx>
Signed-off-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
index e0ae911ef427d..7b69d6dfe44a3 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) {
