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

[Simon Glass]

Hi Stephen,

On Tue, Jan 24, 2012 at 3:14 PM, Stephen Warren <swarren at nvidia.com> wrote:
> 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.

OK I see. I'm not proposing to change U-Boot convention now (if in
fact it has one). At least FDT_GPIO_NONE is a constant that people
need to check against (but they should use fdt_gpio_isvalid()
instead). We can adjust this in the future if U-Boot people want to.

Regards,
Simon
>
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> nvpublic
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