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Date:   Wed, 13 Oct 2021 14:14:37 +0200
From:   Daniel Vetter <daniel@ffwll.ch>
To:     Stephen Boyd <swboyd@chromium.org>
Cc:     Andrzej Hajda <andrzej.hajda@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
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        Arnd Bergmann <arnd@arndb.de>,
        Benjamin Gaignard <benjamin.gaignard@linaro.org>,
        Chen Feng <puck.chen@hisilicon.com>,
        Chen-Yu Tsai <wens@csie.org>,
        Christian Gmeiner <christian.gmeiner@gmail.com>,
        Chun-Kuang Hu <chunkuang.hu@kernel.org>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Emma Anholt <emma@anholt.net>,
        Heiko =?iso-8859-1?Q?St=FCbner?= <heiko@sntech.de>,
        Inki Dae <inki.dae@samsung.com>,
        James Qian Wang <james.qian.wang@arm.com>,
        Jaroslav Kysela <perex@perex.cz>,
        Joerg Roedel <joro@8bytes.org>,
        John Stultz <john.stultz@linaro.org>,
        Joonyoung Shim <jy0922.shim@samsung.com>,
        Jyri Sarha <jyri.sarha@iki.fi>,
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        Philipp Zabel <p.zabel@pengutronix.de>,
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        Rob Clark <robdclark@gmail.com>,
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        Russell King <linux+etnaviv@armlinux.org.uk>,
        Russell King <rmk+kernel@arm.linux.org.uk>,
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        Sebastian Reichel <sre@kernel.org>,
        Seung-Woo Kim <sw0312.kim@samsung.com>,
        Takashi Iwai <tiwai@suse.com>,
        Tian Tao <tiantao6@hisilicon.com>,
        Tomas Winkler <tomas.winkler@intel.com>,
        Tomi Valkeinen <tomba@kernel.org>,
        Will Deacon <will@kernel.org>,
        Xinliang Liu <xinliang.liu@linaro.org>,
        Xinwei Kong <kong.kongxinwei@hisilicon.com>,
        Yong Wu <yong.wu@mediatek.com>
Subject: Re: [PATCH v2 00/34] component: Make into an aggregate bus
Message-ID: <YWbNrfxQ0IqV7vsO@phenom.ffwll.local>
Mail-Followup-To: Stephen Boyd <swboyd@chromium.org>,
        Andrzej Hajda <andrzej.hajda@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org,
        Arnd Bergmann <arnd@arndb.de>,
        Benjamin Gaignard <benjamin.gaignard@linaro.org>,
        Chen Feng <puck.chen@hisilicon.com>, Chen-Yu Tsai <wens@csie.org>,
        Christian Gmeiner <christian.gmeiner@gmail.com>,
        Chun-Kuang Hu <chunkuang.hu@kernel.org>,
        Emma Anholt <emma@anholt.net>,
        Heiko =?iso-8859-1?Q?St=FCbner?= <heiko@sntech.de>,
        Inki Dae <inki.dae@samsung.com>,
        James Qian Wang <james.qian.wang@arm.com>,
        Jaroslav Kysela <perex@perex.cz>, Joerg Roedel <joro@8bytes.org>,
        John Stultz <john.stultz@linaro.org>,
        Joonyoung Shim <jy0922.shim@samsung.com>,
        Jyri Sarha <jyri.sarha@iki.fi>,
        Kai Vehmanen <kai.vehmanen@linux.intel.com>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        linux-fbdev@vger.kernel.org, linux-omap@vger.kernel.org,
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        Lucas Stach <l.stach@pengutronix.de>,
        Mark Brown <broonie@kernel.org>, Maxime Ripard <mripard@kernel.org>,
        Neil Armstrong <narmstrong@baylibre.com>,
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        Philipp Zabel <p.zabel@pengutronix.de>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Rob Clark <robdclark@gmail.com>,
        Russell King <linux@armlinux.org.uk>,
        Russell King <linux+etnaviv@armlinux.org.uk>,
        Russell King <rmk+kernel@arm.linux.org.uk>,
        Sandy Huang <hjc@rock-chips.com>,
        Saravana Kannan <saravanak@google.com>,
        Sebastian Reichel <sre@kernel.org>,
        Seung-Woo Kim <sw0312.kim@samsung.com>,
        Takashi Iwai <tiwai@suse.com>, Tian Tao <tiantao6@hisilicon.com>,
        Tomas Winkler <tomas.winkler@intel.com>,
        Tomi Valkeinen <tomba@kernel.org>, Will Deacon <will@kernel.org>,
        Xinliang Liu <xinliang.liu@linaro.org>,
        Xinwei Kong <kong.kongxinwei@hisilicon.com>,
        Yong Wu <yong.wu@mediatek.com>
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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