Re: [PATCH 0/5] Add of_ functions for device_link_add()

[Dmitry Torokhov]

On Thu, Apr 25, 2019 at 11:08 AM Rob Herring <robh+dt@xxxxxxxxxx> wrote:
>
> On Wed, Apr 24, 2019 at 5:19 AM Benjamin Gaignard
> <benjamin.gaignard@xxxxxx> 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