linux-kernel - Re: [PATCH] drm/amd/display: Fix error code on failure to set brightness

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Date:   Tue, 8 Jun 2021 09:59:59 -0400
From:   Harry Wentland <harry.wentland@....com>
To:     Anand K Mistry <amistry@...gle.com>, amd-gfx@...ts.freedesktop.org
Cc:     Alex Deucher <alexander.deucher@....com>,
        Aurabindo Pillai <aurabindo.pillai@....com>,
        Bas Nieuwenhuizen <bas@...nieuwenhuizen.nl>,
        Christian König <christian.koenig@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>, Eryk Brol <eryk.brol@....com>,
        Leo Li <sunpeng.li@....com>,
        Nicholas Kazlauskas <nicholas.kazlauskas@....com>,
        Nikola Cornij <nikola.cornij@....com>,
        Qingqing Zhuo <qingqing.zhuo@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        Wayne Lin <Wayne.Lin@....com>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/amd/display: Fix error code on failure to set
 brightness

On 2021-06-08 12:32 a.m., Anand K Mistry wrote:
> The backlight_ops.update_status function is required to return a
> negative error code on failure. Returning a positive code may be
> interpreted as a success. This is true for the 'brightness' sysfs file,
> which passes through a non-zero value as the return value of the write()
> syscall. This is interpreted in user-space as a successful write of 1
> character, which is obviously wrong.
> 
> It's not clear exactly what error code to use, but EINVAL should be
> reasonable.
> 
> Signed-off-by: Anand K Mistry <amistry@...gle.com>

Thanks for your patch but this code has changed on amd-staging-drm-next.

Can you try with the latest? The new backlight_update_status will always
return 0 now.

Harry

> ---
> 
>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index 652cc1a0e450..ad322613390d 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -3431,7 +3431,7 @@ static int amdgpu_dm_backlight_update_status(struct backlight_device *bd)
>  	else
>  		rc = dc_link_set_backlight_level(dm->backlight_link, brightness, 0);
>  
> -	return rc ? 0 : 1;
> +	return rc ? 0 : -EINVAL;
>  }
>  
>  static int amdgpu_dm_backlight_get_brightness(struct backlight_device *bd)
>