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

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Date:	Wed, 8 Jun 2016 22:48:23 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Mark Brown <broonie@...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>,
	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 8, 2016 at 8:35 PM, Mark Brown <broonie@...nel.org> wrote:
> 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.

If that's a non-child device, I would expect it to exist beforehand
and then the link creation would only enforce the specific ordering of
certain operations (like runtime PM or async suspend/resume) between
the two devices linked by it.  That shouldn't be problematic in
principle.

Let me redo the series, though (that may take a couple of days realistically).