This is a note to let you know that I've just added the patch titled
drm/radeon: Prefer lower feedback dividers
to the 5.4-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-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 7abad39f34f506b0e75391e3c3dc430ec97bf3d7
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 fc8c70526bd30733ea8667adb8b8ffebea30a8ed ]
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 f9f74150d0d73..e7c4e06bc7d4f 100644
--- a/drivers/gpu/drm/radeon/radeon_display.c
+++ b/drivers/gpu/drm/radeon/radeon_display.c
@@ -932,7 +932,7 @@ 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) {
