linux-kernel - Re: [PATCH] ARM: shmobile: r8a73a4: Move pfc node to work around probe ordering bug

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Message-ID: <20150209182918.GA2531@atomide.com>
Date:	Mon, 9 Feb 2015 10:29:19 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Geert Uytterhoeven <geert+renesas@...der.be>,
	Simon Horman <horms@...ge.net.au>,
	Magnus Damm <magnus.damm@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
	Thierry Reding <thierry.reding@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: shmobile: r8a73a4: Move pfc node to work around
 probe ordering bug

* Geert Uytterhoeven <geert@...ux-m68k.org> [150209 09:17]:
> On Mon, Feb 9, 2015 at 5:24 PM, Tony Lindgren <tony@...mide.com> wrote:
> > * Geert Uytterhoeven <geert+renesas@...der.be> [150206 12:26]:
> >> Notes:
> >>   - It seems several people tried to solve this in the core OF probing
> >>     code before, but the final solution never went in?
> >>   - This can be reproduced on other SoCs (e.g. sh73a0 and r8a7740) by
> >>     moving their pfc nodes before their interrupt controller nodes.
> >>   - This patch is against my working tree, so it doesn't apply to
> >>     Simon's repository, but you get the idea....
> >
> > No issues with the patch, but here are few comments on the core
> > reasons (without looking at the code in this case) that might help
> > fix similar issues.
> >
> > In all the cases I've seen these errors are caused by non-standard
> > custom initcall levels for drivers like i2c bus. The real solution
> > is to initialize drivers later with standard module_init, and stop
> > the race to the bottom with custom initcall levels.
> >
> > If there is legacy board specific platofrm init code that needs
> > i2c gpios early, that code can probably be moved to initialize
> > later on.
> 
> In this case no i2c is involved. The drivers for both pinctrl
> (renesas,pfc-r8a73a4) and irqchip (renesas,irqc) are registered
> at the same level:
>   - postcore_initcall(sh_pfc_init);
>   - postcore_initcall(irqc_init);
> Hence the system uses the "natural" order from within the DTS,
> and decided to instantiate the pfc before the irqchip.

OK
 
> > Also, there should not be any need for custom driver initcall
> > levels from Linux generic framework point of view as for example
> > irqchip implementing drivers work just fine as a loadable module.
> 
> As long as no other device that's instantiated earlier references that
> irqchip?

Right :) And deferred probe won't still remove the warning in
that case. From what I remember, that's a valid warning from irq
framework point of view.

Regards,

Tony
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