linux-kernel - Re: [PATCH v2 00/34] component: Make into an aggregate bus

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Date:   Thu, 7 Oct 2021 12:16:27 +0200
From:   Andrzej Hajda <andrzej.hajda@...il.com>
To:     Stephen Boyd <swboyd@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        Arnd Bergmann <arnd@...db.de>,
        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>,
        Jaroslav Kysela <perex@...ex.cz>,
        Joerg Roedel <joro@...tes.org>,
        John Stultz <john.stultz@...aro.org>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        Jyri Sarha <jyri.sarha@....fi>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        linux-fbdev@...r.kernel.org, linux-omap@...r.kernel.org,
        linux-pm@...r.kernel.org, Liviu Dudau <liviu.dudau@....com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Mark Brown <broonie@...nel.org>,
        Maxime Ripard <mripard@...nel.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Paul Cercueil <paul@...pouillou.net>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Clark <robdclark@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Russell King <linux+etnaviv@...linux.org.uk>,
        Russell King <rmk+kernel@....linux.org.uk>,
        Sandy Huang <hjc@...k-chips.com>,
        Saravana Kannan <saravanak@...gle.com>,
        Sebastian Reichel <sre@...nel.org>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        Takashi Iwai <tiwai@...e.com>,
        Tian Tao <tiantao6@...ilicon.com>,
        Tomas Winkler <tomas.winkler@...el.com>,
        Tomi Valkeinen <tomba@...nel.org>,
        Will Deacon <will@...nel.org>,
        Xinliang Liu <xinliang.liu@...aro.org>,
        Xinwei Kong <kong.kongxinwei@...ilicon.com>,
        Yong Wu <yong.wu@...iatek.com>
Subject: Re: [PATCH v2 00/34] component: Make into an aggregate bus

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/


Regards
Andrzej