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

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Message-ID: <87leiqer8g.fsf@intel.com>
Date:   Mon, 17 Apr 2023 13:29:51 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Jeff Layton <jlayton@...nel.org>, Lyude Paul <lyude@...hat.com>,
        "Lin, Wayne" <Wayne.Lin@....com>,
        Alex Deucher <alexdeucher@...il.com>
Cc:     David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] drm: make drm_dp_add_payload_part2 gracefully handle
 NULL state pointer

On Mon, 17 Apr 2023, Jeff Layton <jlayton@...nel.org> wrote:
> On Mon, 2023-04-17 at 11:44 +0300, Jani Nikula wrote:
>> On Fri, 14 Apr 2023, Lyude Paul <lyude@...hat.com> wrote:
>> > On Fri, 2023-04-14 at 13:35 +0300, Jani Nikula wrote:
>> > > On Fri, 14 Apr 2023, Jeff Layton <jlayton@...nel.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.

I was hoping to lure you into sending patches. ;)

Anyway, I'm not working on this.


BR,
Jani.

>
> Thanks,

-- 
Jani Nikula, Intel Open Source Graphics Center