linux-kernel - Re: [PATCH 0/5] Add of_ functions for device_link

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Message-ID: <CAKdAkRTUsJ4TU7BrSNXCKiQGZnArao9o_qk7i0xSzYJ1SGU14A@mail.gmail.com>
Date:   Thu, 25 Apr 2019 12:24:46 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Benjamin Gaignard <benjamin.gaignard@...com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        Mark Rutland <mark.rutland@....com>,
        Bastien Nocera <hadess@...ess.net>,
        Frank Rowand <frowand.list@...il.com>,
        Marco Felsch <m.felsch@...gutronix.de>,
        Guido Günther <agx@...xcpu.org>,
        Yannick Fertre <yannick.fertre@...com>,
        Arnd Bergmann <arnd@...db.de>,
        Linux Input <linux-input@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-stm32@...md-mailman.stormreply.com,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH 0/5] Add of_ functions for device_link_add()

On Thu, Apr 25, 2019 at 11:08 AM Rob Herring <robh+dt@...nel.org> wrote:
>
> On Wed, Apr 24, 2019 at 5:19 AM Benjamin Gaignard
> <benjamin.gaignard@...com> wrote:
> >
> > It could happen that we need to control suspend/resume ordering between
> > devices without obvious consumer/supplier link. For example when touchscreens
> > and DSI panels share the same reset line, in this case we need to be sure
> > of pm_runtime operations ordering between those two devices to correctly
> > perform reset.
> > DSI panel and touchscreen aren't sharing any heriachical relationship (unlike
> > I2C client and I2C bus or regulator client and regulator provider) so we need
> > to describe this in device-tree.
>
> Needing to know which touchscreen is attached to a panel could be
> important to describe if you have multiple displays.
>
> Doesn't the reset subsystem already have some support for shared
> resets? Seems like it could provide clients with struct device or
> device_node ptrs to other devices sharing a reset.
>
> >
> > This series introduce of_device_links_{add,remove} and devm_of_device_links_add()
> > helpers to find and parse 'links-add' property in a device-tree node.
>
> Going to document that property somewhere? :)
>
> I think this is too generic and coupled to Linux. It doesn't have any
> information as to what is the dependency or connection nor what the
> direction of the dependency is.
>
> I'm not convinced we need to solve this generically vs. defining
> something for this specific example.

I am pretty sure there will be more drivers needing complex
dependencies. Doesn't ACPI allow defining relationship between devices
that goes beyond the tree structure?

Thanks.

-- 
Dmitry