linux-kernel - Re: [RFC PATCH 0/2] DT match helpers for initcalls and platform devices

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Message-Id: <20131121125349.9727DC40A2C@trevor.secretlab.ca>
Date:	Thu, 21 Nov 2013 12:53:49 +0000
From:	Grant Likely <grant.likely@...aro.org>
To:	Rob Herring <robherring2@...il.com>,
	Thierry Reding <thierry.reding@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rob Herring <rob.herring@...xeda.com>
Subject: Re: [RFC PATCH 0/2] DT match helpers for initcalls and platform devices

On Wed, 30 Oct 2013 15:02:40 -0500, Rob Herring <robherring2@...il.com> wrote:
> On Wed, Oct 30, 2013 at 3:26 AM, Thierry Reding
> <thierry.reding@...il.com> wrote:
> > On Wed, Oct 30, 2013 at 01:12:49AM -0500, Rob Herring wrote:
> >> From: Rob Herring <rob.herring@...xeda.com>
> >>
> >> This series adds a couple of boilerplate helpers to match with DT for
> >> initcalls and platform device creation and probe. The goal here is to
> >> remove more platform code out of arch/arm and eventually the machine
> >> descriptors.
> >
> > I fear that this is a step backwards because it makes it easier for
> > people to do the wrong thing. We've been doing the same with interrupt
> > controllers and clocks. With those there's at least the argument that
> > they need to be available really early and therefore cannot use the
> > regular driver model. But for everything else, shouldn't we enforce
> > proper drivers to be written?
> 
> You think both are a step backwards or just the initcall one? For
> initcalls, there are things which are not drivers, but just one time
> init.  The example on highbank is highbank_pm_init. In some cases like
> cpuidle, they have been converted to platform drivers, but then we
> have platform code to create devices if we are on the relevant
> platform. There is not really a real device node that exists for some
> of these drivers and we need to create the device rather than the
> device getting created by scanning the buses in the DT.
> 
> I think this is less error prone because we've had cases of
> unconditional initcalls which break multi-platform kernels.

In that situation, it would probably be better to simply do what you
need to do at initcall level and not register a struct device at all.

If the situation is you absolutely need to create a device because the
DT does not provide what you need (and the DT cannot be changed) then I
strongly recommend separating the driver code and the registration code
into separate blocks because it enforces separation between device
enumaration and device driver probing.

g.

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