[U-Boot] [PATCH v4 03/20] fdt: Add basic support for decoding GPIO definitions

[Stephen Warren]

Simon Glass wrote at Tuesday, January 24, 2012 4:12 PM:
> On Mon, Jan 23, 2012 at 10:18 AM, Stephen Warren <swarren at nvidia.com> wrote:
> > On 01/21/2012 10:08 AM, Simon Glass wrote:
> >> Hi Stephen,
> >>
> >> On Wed, Jan 18, 2012 at 2:17 PM, Stephen Warren <swarren at nvidia.com> wrote:
> >>> On 01/11/2012 09:32 PM, Simon Glass wrote:
> >>>> This adds some support into fdtdec for reading GPIO definitions from
> >>>> the fdt. ...
> > ...
> >>>> diff --git a/include/fdtdec.h b/include/fdtdec.h
> >>> ...
> >>>> +/* GPIOs are numbered from 0 */
> >>>> +enum {
> >>>> +     FDT_GPIO_NONE = -1U,    /* an invalid GPIO used to end our list */
> >>>
> >>> Is this due to the way U-Boot works right now, or something defined by
> >>> this patch? It's been pointed out that the kernel's choice to use -1 as
> >>> "invalid GPIO" rather than 0 was a mistake, since that prevents GPIO
> >>> fields being easily added to platform data structures, since you then
> >>> have to go and initialize every new instance to -1, rather than relying
> >>> on BSS initializing it to 0. I assume this is just the way U-Boot works,
> >>> so solving this is outside the scope of this patch.
> >>
> >> It is nothing to do with U-Boot itself - we can choose any number.
> >
> > Surely the value you choose for DT parsing has to align with the value
> > that U-Boot's GPIO API chooses, so you can't just choose any number.
> 
> No, in the fdt we just leave out the gpio if it is not required. The
> FDT_GPIO_NONE is purely internal to U-Boot.

That's consistent with what I said; I'm talking about the value that a
missing DT property translates into within U-Boot.

-- 
nvpublic