linux-kernel - Re: [PATCH v2 0/7] ARM: berlin: add pinctrl support

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Message-ID: <20140424152620.39eae472@skate>
Date:	Thu, 24 Apr 2014 15:26:20 +0200
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Antoine Ténart 
	<antoine.tenart@...e-electrons.com>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	zhiming Xu <zmxu@...vell.com>,
	Jisheng Zhang <jszhang@...vell.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/7] ARM: berlin: add pinctrl support

Dear Linus Walleij,

On Thu, 24 Apr 2014 14:52:20 +0200, Linus Walleij wrote:

> > Tested on the Berlin BG2Q.
> 
> So now I need some advice from the mvebu pinctrl maintainers
> (Thomas, Sebastian etc):
> 
> - Is this a totally different pin controller so that drivers/pinctrl/mvebu
>  can not be used?

It is. The CPU families are completely different, made from completely
separate divisions of Marvell. Just think that they come from different
companies :-)

On the mvebu side, each pin can be independently configured to a
different function: there is a 4-bits field for each pin to configure
the function.

On the berlin side, pins are only configured in groups. You can't
independently set the functions of each pin: you can set a function to
a pre-defined set of pins.

> - Really?

Yes.

> - OK can you help me review this thing?

Sure. I believe Sebastian already had a very detailed look so he can
provide his review.

> - Should the base folder really be named "berlin" or is this going to
>   be part of a bigger family of pin controllers so a more neutral name
>   should be sought?

berlin is the name of the mach-<foo> directory in arch/arm, and that's
really the code name for this SoC family.

> - Why do hardware engineers seek to reinvent wheels like pin
>   controllers, GPIO and DMA engines all the time :-/

I guess Russell already gave you a good answer to this question :-)

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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