linux-kernel - Re: [PATCH 1/2] drm/amdgpu/mst: Stop ignoring error codes and deadlocking

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Date:   Mon, 14 Nov 2022 16:54:55 -0500
From:   Lyude Paul <lyude@...hat.com>
To:     "Lin, Wayne" <Wayne.Lin@....com>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>
Cc:     "Wentland, Harry" <Harry.Wentland@....com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "Li, Sun peng (Leo)" <Sunpeng.Li@....com>,
        "Siqueira, Rodrigo" <Rodrigo.Siqueira@....com>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        "Kazlauskas, Nicholas" <Nicholas.Kazlauskas@....com>,
        "Pillai, Aurabindo" <Aurabindo.Pillai@....com>,
        "Li, Roman" <Roman.Li@....com>, "Zuo, Jerry" <Jerry.Zuo@....com>,
        "Wu, Hersen" <hersenxs.wu@....com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        "Mahfooz, Hamza" <Hamza.Mahfooz@....com>,
        "Hung, Alex" <Alex.Hung@....com>,
        "Francis, David" <David.Francis@....com>,
        Mikita Lipski <mikita.lipski@....com>,
        "Liu, Wenjing" <Wenjing.Liu@....com>,
        "open list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] drm/amdgpu/mst: Stop ignoring error codes and
 deadlocking

On Wed, 2022-11-09 at 09:48 +0000, Lin, Wayne wrote:
> >   	}
> > -	if (!drm_dp_mst_atomic_check(state) && !debugfs_overwrite) {
> > +	ret = drm_dp_mst_atomic_check(state);
> > +	if (ret == 0 && !debugfs_overwrite) {
> >   		set_dsc_configs_from_fairness_vars(params, vars, count,
> > k);
> > -		return true;
> > +		return 0;
> > +	} else if (ret == -EDEADLK) {
> > +		return ret;
> 
> I think we should return here whenever there is an error. Not just for
> EDEADLK case. 

Are we sure about this one? I think we may actually want to make this so it
returns on ret != -ENOSPC, since we want the function to continue if there's
no space in the atomic state available so it can try recomputing things with
compression enabled. On ret == 0 it should return early without doing
compression, and on ret == -ENOSPC it should just continue the function from
there

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat