linux-kernel - Re: [PATCH] gpio: support for Synopsys DesignWare APB GPIO

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Date:	Sun, 3 Apr 2011 15:07:50 +0100
From:	Jamie Iles <jamie@...ieiles.com>
To:	Anton Vorontsov <cbouatmailru@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Grant Likely <grant.likely@...retlab.ca>,
	Jamie Iles <jamie@...ieiles.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, Nicolas Pitre <nico@...xnic.net>
Subject: Re: [PATCH] gpio: support for Synopsys DesignWare APB GPIO

Hi Anton,

On Sun, Apr 03, 2011 at 04:03:44PM +0400, Anton Vorontsov wrote:
> > > I'm not
> > > hugely thrilled with the current method that the driver uses to define
> > > the register locations (using named resources).  My instinct would be
> > > to use a single register resource region with offsets for each
> > > register type defined from the base of it, but Anton can probably fill
> > > us in on the reason that approach was used.
> 
> Well, I did it that way because you don't have to pass the offsets via
> platform data (you don't need platform data most of the time, i.e. if
> you use dynamic bases).

Well I'm happy to give it a go for some more complex chips with multiple 
banks but I'm not sure how to accomplish this without platform data.  My 
first idea would be to have something like:

struct mmio_gpio_bank {
	unsigned int		ngpio;
	unsigned long		set_offs;
	unsigned long		clr_offs;
	unsigned long		dout_offs;
	unsigned long		din_offs;
	unsigned long		dir_offs;
};

struct mmio_gpio_pdata {
	size_t			bus_width_bits;
	int			gpio_base;
	unsigned int		nr_banks;
	struct mmio_gpio_bank	banks[];
};

and have one iomem resource for the whole controller.  This allows us to 
cope with the controllers where each bank has a different number of GPIO 
pins but I'm not sure how device tree friendly it is.  If there's a 
better way then please let me know and I'll give it a go, though
at first it does need to be able to work without device tree support.

Looking at some of the different IRQ demuxing schemes they seem to vary 
quite a bit so I'm not sure how to handle that in a relatively generic 
way but perhaps that can come later.

Jamie
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