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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:     Jani Nikula <jani.nikula@linux.intel.com>,
        Lyude Paul <lyude@redhat.com>,
        "Lin, 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" <linux-kernel@vger.kernel.org>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>
Date:   Mon, 17 Apr 2023 06:06:37 -0400
In-Reply-To: <874jpegao0.fsf@intel.com>
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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 create MST payload for po=
rt" indicates
> > > > > error while configuring DPCD 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 loggi=
ng?
> > > >=20
> > > > Note that this problem is _very_ intermittent too: I went about 2 w=
eeks
> > > > between crashes, and then I got 3 in one day. I'd rather not run wi=
th a
> > > > lot of debug logging for a long time if that's what this is going t=
o
> > > > require, as this is my main workstation.
> > > >=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 ju=
st
> > > > categorically wrong for the caller to pass down a NULL state pointe=
r 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") a=
nd
> > > its only use is to get at state->dev for debug logging.
> > >=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 certainly 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 entirely
>=20
> I guess we could use two patches then, first replace state->dev with
> mgr->dev as something that can be backported as needed, and second drop
> the state parameter altogether.
>=20
> Jeff, up for it? At least the first one?
>=20
>=20
> BR,
> Jani.
>=20

Sure. I'm happy to test patches if you send them along.

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