Hi Stephen,
On Mon, Jan 23, 2012 at 10:18 AM, Stephen Warren swarren@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@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.
What is Linux using now / planning to use?
Linux uses -1 right now, but should really have used 0. I don't think there's an actual plan to change this now, since the numbering scheme is entrenched.
What Linux does isn't relevant; the numbering scheme I'm talking about is the internal numbering scheme within U-Boot or Linux, which are independent from each-other and the values in the device tree.
So that said, I was wondering if U-Boot's GPIO support (covering both non-DT and DT cases) was new enough that it could use 0 to represent "invalid GPIO" rather than -1, and hence FDT_GPIO_NONE be 0 not -1. It probably isn't though; I guess U-Boot's GPIO numbering scheme is also already entrenched?
Yes it starts at zero. I'm not sure how to even begin such a discussion on the list :-)
Regards, Simon
-- nvpublic