[PATCH] drm: make drm_dp_add_payload_part2 gracefully handle NULL state pointer

[Lin, Wayne]

[Public]

Hi Jeff,

Thanks. I might need more information to understand why we can't retrieve
the drm atomic state. Also , "Failed to create MST payload for port" indicates
error while configuring DPCD payload ID table. Could you help to provide log
with KMS + ATOMIC + DP debug on please? Thanks in advance!

Regards,
Wayne

> -----Original Message-----
> From: Alex Deucher <alexdeucher at gmail.com>
> Sent: Thursday, April 13, 2023 8:59 PM
> To: Jani Nikula <jani.nikula at linux.intel.com>; Lin, Wayne
> <Wayne.Lin at amd.com>
> Cc: Jeff Layton <jlayton at kernel.org>; David Airlie <airlied at gmail.com>;
> Daniel Vetter <daniel at ffwll.ch>; Deucher, Alexander
> <Alexander.Deucher at amd.com>; linux-kernel at vger.kernel.org; dri-
> devel at lists.freedesktop.org
> Subject: Re: [PATCH] drm: make drm_dp_add_payload_part2 gracefully
> handle NULL state pointer
> 
> + Wayne
> 
> On Thu, Apr 13, 2023 at 8:31 AM Jani Nikula <jani.nikula at linux.intel.com>
> wrote:
> >
> > On Thu, 13 Apr 2023, Jeff Layton <jlayton at kernel.org> wrote:
> > > I've been experiencing some intermittent crashes down in the display
> > > driver code. The symptoms are ususally a line like this in dmesg:
> > >
> > >     amdgpu 0000:30:00.0: [drm] Failed to create MST payload for port
> > > 000000006d3a3885: -5
> > >
> > > ...followed by an Oops due to a NULL pointer dereference.
> > >
> > > The real bug is probably in the caller of this function, which is
> > > passing it a NULL state pointer, but this patch at least keeps my
> > > machine from oopsing when this occurs.
> >
> > My fear is that papering over this makes the root cause harder to find.
> >
> > Cc: Harry, Alex
> >
> >
> > BR,
> > Jani.
> >
> >
> > >
> > > Link: https://bugzilla.redhat.com/show_bug.cgi?id=2184855
> > > Signed-off-by: Jeff Layton <jlayton at kernel.org>
> > > ---
> > >  drivers/gpu/drm/display/drm_dp_mst_topology.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > > b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > > index 38dab76ae69e..87ad406c50f9 100644
> > > --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > > +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> > > @@ -3404,7 +3404,8 @@ int drm_dp_add_payload_part2(struct
> > > drm_dp_mst_topology_mgr *mgr,
> > >
> > >       /* Skip failed payloads */
> > >       if (payload->vc_start_slot == -1) {
> > > -             drm_dbg_kms(state->dev, "Part 1 of payload creation for %s
> failed, skipping part 2\n",
> > > +             drm_dbg_kms(state ? state->dev : NULL,
> > > +                         "Part 1 of payload creation for %s failed,
> > > + skipping part 2\n",
> > >                           payload->port->connector->name);
> > >               return -EIO;
> > >       }
> >
> > --
> > Jani Nikula, Intel Open Source Graphics Center