linux-kernel - Re: [PATCH 1/4 v4] drivers: create a pin control subsystem

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Date:	Mon, 22 Aug 2011 13:54:08 +0100
From:	Jamie Iles <jamie@...ieiles.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Jamie Iles <jamie@...ieiles.com>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Grant Likely <grant.likely@...retlab.ca>,
	Stephen Warren <swarren@...dia.com>,
	Russell King <linux@....linux.org.uk>,
	Joe Perches <joe@...ches.com>,
	Linaro Dev <linaro-dev@...ts.linaro.org>,
	Lee Jones <lee.jones@...aro.org>, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 1/4 v4] drivers: create a pin control subsystem

On Mon, Aug 22, 2011 at 02:38:16PM +0200, Linus Walleij wrote:
> On Sun, Aug 21, 2011 at 4:24 PM, Jamie Iles <jamie@...ieiles.com> wrote:
> 
> > for device tree, when the gpio
> > controllers are registered, the base is typically dynamically assigned.  I
> > suspect that this can be solved in the device tree binding for the controller
> > that references the bindings of the pinctrl, but this would require
> > registering the gpio_ranges at runtime (or at least the bases).
> 
> Oh registering ranges at runtime ... crap. But possible I think.
> 
> > So perhaps if we had:
> >
> > struct pinctrl_gpio_range {
> >    unsigned int pinctrl_base;
> >    struct gpio_chip *chip;
> > }
> >
> > and then gpio_request_enable was:
> >
> > int (*gpio_request_enable)(struct pinctrl_dev *pctldev,
> >                           struct gpio_chip *gc,
> >                           unsigned offset)
> >
> > Then have pinctrl_register_gpio_chip()?
> 
> I'm not following - the struct gpio_chip is opaque outside the gpio
> subsystem, I've proposed patches to make it public but they have
> been NAK:ed.
> 
> Which means pinctrl has no use of that pointer.
> 
> What is the intended purpose of sending that thing in?

Well even though the gpio_chip is opaque to pinctrl, the pointer can 
still be used for searching, which means that gpio_request() doesn't 
need to know the integer instance number (which would presumably be 
passed with platform_data for non-DT?).

> Right now my range struct looks like this:
> 
> /**
>  * struct pinctrl_gpio_range - each pin controller can provide subranges of
>  * the GPIO number space to be handled by the controller
>  * @name: a name for the chip in this range
>  * @id: an ID number for the chip in this range
>  * @base: base offset of the GPIO range
>  * @npins: number of pins in the GPIO range, including the base number
>  */
> struct pinctrl_gpio_range {
>         const char name[16];
>         unsigned int id;
>         unsigned int base;
>         unsigned int npins;
> };
> 
> > For the static devices case then we can require gc->base must match the
> > pinctrl gpio base. For the device tree case we could do some matching of
> > device_nodes from the gpio_chip to the pinctrl definitions?
> 
> Can't do that since we can't look into struct gpio_chip intrinsics...
> 
> But we can register ranges at runtime, I'll just make the pin controller keep
> a list of GPIO ranges, simple.

OK, I do think it would be nice to use a gpio_chip based request, but I 
don't want to create too many obstacles for getting this code merged!

Jamie
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