Re: Patch "drm/radeon: Prefer lower feedback dividers" has been added to the 5.9-stable tree

Re: Patch "drm/radeon: Prefer lower feedback dividers" has been added to the 5.9-stable tree

[Kai-Heng Feng]

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) {

Re: Patch "drm/radeon: Prefer lower feedback dividers" has been added to the 5.9-stable tree

[Sasha Levin]

On Mon, Oct 26, 2020 at 01:13:28PM +0800, Kai-Heng Feng wrote:
>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.

Will do, thanks!

-- 
Thanks,
Sasha