Re: [RFC Patch] gpio: add GPIO hogging mechanism

Benoit Parrot
2014-11-04T00:38:33Z

Linus,

Thanks for the feedback.

To summarize the hog feature should be local to gpiolib-of.c, correct?

I also also need some clarifications, see below.

Linus Walleij <linus.walleij@linaro.org> wrote on Mon [2014-Nov-03 10:59:53 +0100]:
> On Tue, Oct 21, 2014 at 10:09 PM, Benoit Parrot <bparrot@ti.com> wrote:
>
> > qe_pio_a: gpio-controller@1400 {
> > @@ -110,6 +130,19 @@ Example of two SOC GPIO banks defined as gpio-controller nodes:
> > reg = <0x1400 0x18>;
> > gpio-controller;
> > #gpio-cells = <2>;
> > + gpio-hogs = <&line_b>;
> > +
> > + /* line_a hog is defined but not enabled in this example*/
> > + line_a: line_a {
> > + gpios = <5 0>;
> > + input;
> > + };
> > +
> > + line_b: line_b {
> > + gpios = <6 0>;
> > + output-low;
> > + line-name = "foo-bar-gpio";
> > + };
>
>
> I don't see the point of having unused hogs and enabling them using
> phandles.
>
> Just let the core walk over all children nodes of a GPIO controller
> and hog them. Put in a bool property saying it's a hog.
>
> + line_b: line_b {
> + gpio-hog;
> + gpios = <6 0>;
> + output-low;
> + line-name = "foo-bar-gpio";
> + };
>
> I don't quite see the point with input hogs that noone can use
> but whatever.
>
> I am thinking that maybe the line name should be compulsory
> so as to improbe readability. I mean there is always a reason
> why you're hogging a pin and the name should say it.

Ok, so as an alternative I had presented something like this in my reply
to Alexandre Courbot's review comments:

I did consider a "pinmux" flavored format (not sure how hard to parse it would be).
It would allow grouping if nothing else.

/* Line syntax: line_name <gpio# flags> direction-value [export] */
gpio-hogs = <&group_y>;

group_y: group_y {
gpio-hogs-group = <
line_x <15 0> output-low
line_y <16 0> output-high export
line_z <17 0> input
>;
};

Now based on your comment would something like this work?

qe_pio_a: gpio-controller@1400 {
reg = <0x1400 0x18>;
gpio-controller;
#gpio-cells = <2>;

/* Line syntax: line_name <gpio# flags> direction-value [export] */
gpio-hogs: {
gpio-hogs-group = <
foo-bar-gpio <15 0> output-low
bar-foo-gpio <16 0> output-high export
>;
};
};

This would group all hogs for one controller under a single child node.
Again I am not sure how feasible or easy to implement the DT parsing would be.

I guess for completeness if you could also comment on my reply to Alexandre from Oct 29th,
that would be great, before I head in the wrong directions.

Regards,
Benoit