* Re: Patch "drm/radeon: Prefer lower feedback dividers" has been added to the 5.9-stable tree
[not found] <20201026050946.9E8B6223FD@mail.kernel.org>
@ 2020-10-26 5:13 ` Kai-Heng Feng
2020-10-26 14:38 ` Sasha Levin
0 siblings, 1 reply; 2+ messages in thread
From: Kai-Heng Feng @ 2020-10-26 5:13 UTC (permalink / raw)
To: Sasha Levin; +Cc: stable-commits, linux-stable
Hi Sasha,
> On Oct 26, 2020, at 13:09, Sasha Levin <sashal@kernel.org> wrote:
>
> 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@vger.kernel.org> know about it.
Please drop this patch because it causes some regression.
Kai-Heng
>
>
>
> commit 3fa04dfbb55a95e7c6075d0644f64bcb6e7f4ef8
> Author: Kai-Heng Feng <kai.heng.feng@canonical.com>
> 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@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>
>
> 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) {
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