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

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Date:	Thu, 14 Feb 2013 13:22:22 +0100
From:	Lars Poeschel <poeschel@...onage.de>
To:	Linus Walleij <linus.walleij@...aro.org>
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 Wednesday 13 February 2013 at 13:51:12, Linus Walleij wrote:
> 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?

No, I haven't. And although this doesn't solve all my problems, I like the 
idea very much! Thank you for this! But at the moment it looks to me that 
this could be a bit overkill for setting this single register and I don't 
think this is, what Grant meant me to do. 
Anyway, I will have a deeper look at this.

Thanks,
Lars
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