diff mbox series

[5.8,101/186] drm/radeon: Prefer lower feedback dividers

Message ID 20200908152246.531365310@linuxfoundation.org
State Superseded
Headers show
Series None | expand

Commit Message

Greg KH Sept. 8, 2020, 3:24 p.m. UTC 
From: Kai-Heng Feng <kai.heng.feng@canonical.com>

[ 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@amd.com>
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/radeon/radeon_display.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Greg KH Sept. 9, 2020, 11:24 a.m. UTC | #1 
On Wed, Sep 09, 2020 at 01:15:13PM +0200, Christian König wrote:
> Hi Greg,
> 
> please drop that patch. It turned out to break a lot of different setups and
> we are going to revert it now.

Ok, now dropped from all trees, thanks.

greg k-h
diff mbox series

Patch

diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
index df1a7eb736517..840c4bf6307fd 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) {