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

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Date:   Thu, 25 Apr 2019 13:07:53 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Benjamin Gaignard <benjamin.gaignard@...com>
Cc:     "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.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>,
        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 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.

Rob