linux-kernel - Re: [PATCH] drm/amd/display: Fix error returned by program_hpd

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Date:   Tue, 31 Dec 2019 10:08:29 -0500
From:   Harry Wentland <hwentlan@....com>
To:     Aditya Pakki <pakki001@....edu>
Cc:     kjlu@....edu, Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "David (ChunMing) Zhou" <David1.Zhou@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Bhawanpreet Lakha <Bhawanpreet.Lakha@....com>,
        Anthony Koo <Anthony.Koo@....com>, Jun Lei <Jun.Lei@....com>,
        David Francis <David.Francis@....com>,
        Eric Yang <Eric.Yang2@....com>,
        Nikola Cornij <nikola.cornij@....com>,
        Eric Bernstein <eric.bernstein@....com>,
        Chris Park <Chris.Park@....com>,
        Wenjing Liu <Wenjing.Liu@....com>,
        David Galiffi <david.galiffi@....com>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/amd/display: Fix error returned by program_hpd_filter

On 2019-11-17 12:22 p.m., Aditya Pakki wrote:
> program_hpd_filter() currently fails to check for the errors
> returned in construct(). This patch returns error in
> case of failure.
> 
> Signed-off-by: Aditya Pakki <pakki001@....edu>
> ---
>  drivers/gpu/drm/amd/display/dc/core/dc_link.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link.c b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
> index ca20b150afcc..bbb648a50c41 100644
> --- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
> +++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
> @@ -1379,9 +1379,8 @@ static bool construct(
>  	 * If GPIO isn't programmed correctly HPD might not rise or drain
>  	 * fast enough, leading to bounces.
>  	 */
> -	program_hpd_filter(link);
> +	return program_hpd_filter(link);

We don't want program_hpd_filter to become a fatal error, which this
would do.

Though it would be good to print a warning if program_hpd_filter fails
as it's unexpected and might lead to bugs with some displays. In many
cases failing to program the HPD filter won't lead to adverse behavior.

Harry

>  
> -	return true;
>  device_tag_fail:
>  	link->link_enc->funcs->destroy(&link->link_enc);
>  link_enc_create_fail:
>