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Subject: Re: [PATCH] drm: make drm_dp_add_payload_part2 gracefully handle
 NULL state pointer
From:   Jeff Layton <jlayton@kernel.org>
To:     "Lin, Wayne" <Wayne.Lin@amd.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Lyude Paul <lyude@redhat.com>,
        Alex Deucher <alexdeucher@gmail.com>
Cc:     David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
        "Deucher, Alexander" <Alexander.Deucher@amd.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>
Date:   Mon, 17 Apr 2023 07:13:44 -0400
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On Mon, 2023-04-17 at 10:58 +0000, Lin, Wayne wrote:
> [AMD Official Use Only - General]
>=20
>=20
>=20
> > -----Original Message-----
> > From: Jani Nikula <jani.nikula@linux.intel.com>
> > Sent: Monday, April 17, 2023 6:30 PM
> > To: Jeff Layton <jlayton@kernel.org>; Lyude Paul <lyude@redhat.com>; Li=
n,
> > Wayne <Wayne.Lin@amd.com>; Alex Deucher <alexdeucher@gmail.com>
> > Cc: David Airlie <airlied@gmail.com>; Daniel Vetter <daniel@ffwll.ch>;
> > Deucher, Alexander <Alexander.Deucher@amd.com>; linux-
> > kernel@vger.kernel.org; dri-devel@lists.freedesktop.org
> > Subject: Re: [PATCH] drm: make drm_dp_add_payload_part2 gracefully
> > handle NULL state pointer
> >=20
> > On Mon, 17 Apr 2023, Jeff Layton <jlayton@kernel.org> wrote:
> > > On Mon, 2023-04-17 at 11:44 +0300, Jani Nikula wrote:
> > > > On Fri, 14 Apr 2023, Lyude Paul <lyude@redhat.com> wrote:
> > > > > On Fri, 2023-04-14 at 13:35 +0300, Jani Nikula wrote:
> > > > > > On Fri, 14 Apr 2023, Jeff Layton <jlayton@kernel.org> wrote:
> > > > > > > On Fri, 2023-04-14 at 04:40 +0000, Lin, Wayne wrote:
> > > > > > > > [Public]
> > > > > > > >=20
> > > > > > > > Hi Jeff,
> > > > > > > >=20
> > > > > > > > Thanks. I might need more information to understand why we
> > > > > > > > can't retrieve the drm atomic state. Also , "Failed to crea=
te
> > > > > > > > MST payload for port" indicates error while configuring DPC=
D
> > > > > > > > payload ID table. Could you help to provide log with KMS +
> > ATOMIC + DP debug on please? Thanks in advance!
> > > > > > > >=20
> > > > > > > > Regards,
> > > > > > > > Wayne
> > > > > > > >=20
> > > > > > >=20
> > > > > > > Possibly. I'm not that familiar with display driver debugging=
.
> > > > > > > Can you send me some directions on how to crank up that sort =
of
> > debug logging?
> > > > > > >=20
> > > > > > > Note that this problem is _very_ intermittent too: I went abo=
ut
> > > > > > > 2 weeks between crashes, and then I got 3 in one day. I'd
> > > > > > > rather not run with a lot of debug logging for a long time if
> > > > > > > that's what this is going to require, as this is my main work=
station.
> > > > > > >=20
> > > > > > > The last time I got this log message, my proposed patch did
> > > > > > > prevent the box from oopsing, so I'd really like to see it go
> > > > > > > in unless it's just categorically wrong for the caller to pas=
s
> > > > > > > down a NULL state pointer to drm_dp_add_payload_part2.
> > > > > >=20
> > > > > > Cc: Lyude.
> > > > > >=20
> > > > > > Looks like the state parameter was added in commit 4d07b0bc4034
> > > > > > ("drm/display/dp_mst: Move all payload info into the atomic
> > > > > > state") and its only use is to get at state->dev for debug logg=
ing.
> > > > > >=20
> > > > > > What's the plan for the parameter? Surely something more than
> > > > > > that! :)
> > > > >=20
> > > > > I don't think there was any plan for that, or at least I certainl=
y
> > > > > don't even remember adding that D:. It must totally have been by
> > > > > mistake and snuck by review, if that's the only thing that we're
> > > > > using it for I'd say it's definitely fine to just drop it entirel=
y
> > > >=20
> > > > I guess we could use two patches then, first replace state->dev wit=
h
> > > > mgr->dev as something that can be backported as needed, and second
> > > > mgr->drop
> > > > the state parameter altogether.
> > > >=20
> > > > Jeff, up for it? At least the first one?
> > > >=20
> > > >=20
> > > > BR,
> > > > Jani.
> > > >=20
> > >=20
> > > Sure. I'm happy to test patches if you send them along.
> >=20
> > I was hoping to lure you into sending patches. ;)
> >=20
> > Anyway, I'm not working on this.
> >=20
> >=20
> Hi Jeff,
>=20
> I probably know the root cause.=20
> But it doesn't need to use the state in the end, I will just rely on the =
patch=20
> that Jani suggested to fix it. I can help to provide the patch later : )
>=20
>=20

Sounds good. If you want to send me a patch to solve the root cause,
I'll put it in the kernel with the other one I'm testing.

Thanks,
--=20
Jeff Layton <jlayton@kernel.org>