Message-ID: <YWbNrfxQ0IqV7vsO@phenom.ffwll.local>
Date:   Wed, 13 Oct 2021 14:14:37 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Andrzej Hajda <andrzej.hajda@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
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        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Chen Feng <puck.chen@...ilicon.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Emma Anholt <emma@...olt.net>,
        Heiko Stübner <heiko@...ech.de>,
        Inki Dae <inki.dae@...sung.com>,
        James Qian Wang <james.qian.wang@....com>,
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Subject: Re: [PATCH v2 00/34] component: Make into an aggregate bus

On Thu, Oct 07, 2021 at 04:46:22PM -0400, Stephen Boyd wrote:
> Quoting Andrzej Hajda (2021-10-07 03:16:27)
> > Hi Stephen,
> >
> > On 06.10.2021 21:37, Stephen Boyd wrote:
> > > This series is from discussion we had on reordering the device lists for
> > > drm shutdown paths[1]. I've introduced an 'aggregate' bus that we put
> > > the aggregate device onto and then we probe the aggregate device once
> > > all the components are probed and call component_add(). The probe/remove
> > > hooks are where the bind/unbind calls go, and then a shutdown hook is
> > > added that can be used to shutdown the drm display pipeline at the right
> > > time.
> > >
> > > This works for me on my sc7180 board. I no longer get a warning from i2c
> > > at shutdown that we're trying to make an i2c transaction after the i2c
> > > bus has been shutdown. There's more work to do on the msm drm driver to
> > > extract component device resources like clks, regulators, etc. out of
> > > the component bind function into the driver probe but I wanted to move
> > > everything over now in other component drivers before tackling that
> > > problem.
> >
> >
> > As I understand you have DSI host with i2c-controlled DSI bridge. And
> > there is an issue that bridge is shutdown before msmdrm. Your solution
> > is to 'adjust' device order on pm list.
> > I had similar issue and solved it locally by adding notification from
> > DSI bridge to DSI host that is has to be removed: mipi_dsi_detach, this
> > notification escalates in DSI host to component_del and this allow to
> > react properly.
> >
> > Advantages:
> > - it is local (only involves DSI host and DSI device),
> > - it does not depend on PM internals,
> > - it can be used in other scenarios as well - unbinding DSI device driver
> >
> > Disadvantage:
> > - It is DSI specific (but this is your case), I have advertised some
> > time ago more general approach [1][2].
> >
> > [1]: https://static.sched.com/hosted_files/osseu18/0f/deferred_problem.pdf
> > [2]: https://lwn.net/Articles/625454/
> >
> 
> I think these are all points for or against using the component code in
> general? Maybe you can send patches that you think can solve the problem
> I'm experiencing and we can review them on the list.

Yeah I think this is entirely orthogonal. If you use component, then
component should provide a way to handle this.

If you use something else, like drm_bridge or dsi or whatever, then that
part should provide a solution to stage stuff correctly and handle all the
ordering.

Now there's a bunch of drivers which mix up component with bridge use and
hilarity ensues, but since there's no real effort to fix that I think it's
toally fine to just improve component.c meanwhile.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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