linux-kernel - Re: [RFC][PATCH 2/5] driver core: Functional dependencies tracking support

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Message-ID: <20160608183535.GP7510@sirena.org.uk>
Date:	Wed, 8 Jun 2016 19:35:35 +0100
From:	Mark Brown <broonie@...nel.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Grant Likely <grant.likely@...aro.org>,
	Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	Thierry Reding <treding@...dia.com>,
	Dmitry Torokhov <dtor@...gle.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Michael Turquette <mturquette@...libre.com>
Subject: Re: [RFC][PATCH 2/5] driver core: Functional dependencies tracking
 support

On Wed, Jun 08, 2016 at 08:12:34PM +0200, Rafael J. Wysocki wrote:
> On Wed, Jun 8, 2016 at 2:48 PM, Mark Brown <broonie@...nel.org> wrote:
> > On Thu, Jan 14, 2016 at 02:54:17AM +0100, Rafael J. Wysocki wrote:

> >> + * A side effect of the link creation is re-ordering of dpm_list and the
> >> + * devices_kset list by moving the consumer device and all devices depending
> >> + * on it to the ends of those lists.

> > How does this work in the scenario where a device instantiates a child
> > device then uses services that child provides to complete the
> > initializiation?  We do have that scenario currently for on chip
> > regulators to allow external regulators to be used.

> I'm not sure I understand the question correctly, but it that is the
> parent and a child, we don't need an extra link entity to represent
> that dependency, as parent-child dependencies are taken by the current
> code into account already.

A parent (especially a MFD) may create a child to fulfil a role that
could also be filled by a non-parent device, if that happens then
depending on what ends up creating these links (it's not 100% clear from
this series) it's likely that the link creation will also end up
registering a dependency unless we do something special.  Now I think
about it this does depend on how we create the children though, it's
less likely to be an issue if the dependencies are created by firmware
code.

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