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

[Jeff Layton <jlayton@kernel.org>]

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]
> > > > > 
> > > > > 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
> > > > > 
> > > > 
> > > > 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?
> > > > 
> > > > Note that this problem is _very_ intermittent too: I went about 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 workstation.
> > > > 
> > > > 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 pass down a NULL state pointer to
> > > > drm_dp_add_payload_part2.
> > > 
> > > Cc: Lyude.
> > > 
> > > 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 logging.
> > > 
> > > What's the plan for the parameter? Surely something more than that! :)
> > 
> > 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
> 
> 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.
> 
> Jeff, up for it? At least the first one?
> 
> 
> BR,
> Jani.
> 

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

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