linux-kernel - Re: [PATCH v4 03/10] pinctrl: mvebu: kirkwood pinctrl driver

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Date:	Thu, 20 Sep 2012 21:28:20 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Andrew Lunn <andrew@...n.ch>,
	Russell King <linux@....linux.org.uk>,
	Jason Cooper <jason@...edaemon.net>,
	Stephen Warren <swarren@...dotorg.org>,
	devicetree-discuss@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Rob Herring <rob.herring@...xeda.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Lior Amsalem <alior@...vell.com>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	Rob Landley <rob@...dley.net>,
	Gregory CLEMENT <gregory.clement@...e-electrons.com>
Subject: Re: [PATCH v4 03/10] pinctrl: mvebu: kirkwood pinctrl driver

On Thu, Sep 20, 2012 at 5:30 PM, Arnd Bergmann <arnd@...db.de> wrote:

> A corner case is the one where you have different versions of the same
> IP block (e.g. the pinctrl) and the kernel cannot find out which one it
> is by looking at registers inside it or on the parent bus, but only
> by looking at other hardware (CPU core revision, or PCI device ID of
> the root complex).

So this is the case I'm thinking of. We have e.g. differens small flags
through platform data depending on cpu_is_ux* in the ux500.

Currently we modify platform data in the board files, just as we
switch some cache handling etc as we know this or that
ASIC has different sized cache.

> We have a precedent of at91 doing this, but I don't
> like it too much because that still means having to change the driver
> again if you get a new SoC with the same IP block but a different version
> register,

I don't like that either.

> To avoid that, I'd prefer using separate "compatible"
> values, at least if the hardware is already described in separate .dtsi
> files.

So what I'm after is whether in this case statically encoding this
onto the .dtsi files is the right thing to do, or whether the boot loader
or kernel should runtime-modify the device tree, patching in
the ASIC-specific info, just like device tree files can override
properties from include files.

Or if this is a bad idea.

Nobody is doing that right now AFAICT, but it is surely possible....

Yours,
Linus Walleij
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