what is the rationale for funny "0x100" offset for OMAP4 GPIO addresses?

[Robert P. J. Day]

On Wed, 5 Dec 2012, Sascha Hauer wrote:

> On Wed, Dec 05, 2012 at 07:54:51AM -0500, Robert P. J. Day wrote:
> >
> >   i was going to submit a patch to replace magic constants for OMAP4
> > with more meaningful names but i ran into an oddity.  here's
> > omap4-silicon.h:
> >
> > #define OMAP44XX_L4_WKUP_BASE           0x4A300000
> > #define OMAP44XX_L4_PER_BASE            0x48000000
> >
> > and here's part of an old posting to the linux-omap mailing list:
> >
> > +/* GPIO controller*/
> > +#define OMAP44XX_GPIO1_BASE             (L4_WK_44XX_BASE  + 0x10000)
> > +#define OMAP44XX_GPIO2_BASE             (L4_PER_44XX_BASE + 0x55000)
> > +#define OMAP44XX_GPIO3_BASE             (L4_PER_44XX_BASE + 0x57000)
> > +#define OMAP44XX_GPIO4_BASE             (L4_PER_44XX_BASE + 0x59000)
> > +#define OMAP44XX_GPIO5_BASE             (L4_PER_44XX_BASE + 0x5B000)
> > +#define OMAP44XX_GPIO6_BASE             (L4_PER_44XX_BASE + 0x5D000)
> >
> > but here's the tail end of omap4-generic.c:
> >
> > static int omap4_gpio_init(void)
> > {
> >         add_generic_device("omap-gpio", 0, NULL, 0x4a310100,
> >                                 0xf00, IORESOURCE_MEM, NULL);
> >         add_generic_device("omap-gpio", 1, NULL, 0x48055100,
> >                                 0xf00, IORESOURCE_MEM, NULL);
> >         add_generic_device("omap-gpio", 2, NULL, 0x48057100,
> >                                 0xf00, IORESOURCE_MEM, NULL);
> >         add_generic_device("omap-gpio", 3, NULL, 0x48059100,
> >                                 0xf00, IORESOURCE_MEM, NULL);
> >         add_generic_device("omap-gpio", 4, NULL, 0x4805b100,
> >                                 0xf00, IORESOURCE_MEM, NULL);
> >         add_generic_device("omap-gpio", 5, NULL, 0x4805d100,
> >                                 0xf00, IORESOURCE_MEM, NULL);
> >
> >         return 0;
> > }
> >
> >   as you can see, the numbers don't add up exactly -- the
> > constants in that final file are all 0x100 larger than a simple
> > addition.  anyone know where that comes from?
>
> This comes from the hardware. The GPIO controller is the same as on
> omap3, but the base addresses have an additional 0x100 offset.

  ah, gotcha.  so i'll throw together a patch that changes those
numbers to appropriate macro names as i did for omap3, just for
readability.

rday

-- 

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Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

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