linux-kernel - Re: [PATCH v2] gpio: mcp23s08: convert driver to DT

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Date:	Wed, 13 Feb 2013 13:51:12 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Lars Poeschel <poeschel@...onage.de>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Lars Poeschel <larsi@....tu-dresden.de>,
	rob.herring@...xeda.com, rob@...dley.net,
	devicetree-discuss@...ts.ozlabs.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	spi-devel-general@...ts.sourceforge.net
Subject: Re: [PATCH v2] gpio: mcp23s08: convert driver to DT

On Wed, Feb 13, 2013 at 12:13 PM, Lars Poeschel <poeschel@...onage.de> wrote:
> On Monday 11 February 2013 at 22:25:51, Grant Likely wrote:
>>
>> However, is the pullup selection per-gpio line? If so, then why not
>> encode it into the flags field of the gpio specifier?
>
> Yes, the pullup is per-gpio line. I am working on that. It turns out, that
> this is a bit difficult for me, as there is no real documentation and no
> other driver is doing it or something similar yet. Exception are very few
> gpio soc drivers where situation is a bit different. They seem to rely an
> fixed global gpio numbers and they are always memory mapped.
> But as I said I am working on it...

Part of your problem is that pull-up is pin control territory.

We invented that subsystem for a reason, and that reason
was that the GPIO subsystem had a hard time accomodating
things like this.

If you look in drivers/pinctrl/pinctrl-abx500.c which is my
latest submitted pinctrl driver you can see that this is basically
a quite simple GPIO chip, we just model it as a pin controller
with a GPIO front-end too exactly because it can do things
like multiplexing, pull-up and pull-down.

Have you considered this approach?

Yours,
Linus Walleij
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