Re: [PATCH 1/3] Device tree binding documentation for gpio-switch

[Martyn Welch]

On 07/12/15 17:37, Rob Herring wrote:
> +Linus W
>
> On Fri, Dec 04, 2015 at 05:31:13PM +0000, Martyn Welch wrote:
> > This patch adds documentation for the gpio-switch binding. This binding
> > provides a mechanism to bind named links to gpio, with the primary
> > purpose of enabling standardised access to switches that might be standard
> > across a group of devices but implemented differently on each device.
>
> This is good and what I suggested, but it now makes me wonder if switch
> is generic enough. This boils down to needing to expose single gpio
> lines to userspace with a defined function/use. IIRC, there's been some
> discussion about this before along with improving the userspace
> interface for GPIO in general. So I'd like to get Linus' thoughts on
> this.

No problem. Rename gpio-signal?

> > Signed-off-by: Martyn Welch <martyn.welch@xxxxxxxxxxxxxxx>
> > ---
> >   .../devicetree/bindings/misc/gpio-switch.txt       | 47 ++++++++++++++++++++++
> >   1 file changed, 47 insertions(+)
> >   create mode 100644 Documentation/devicetree/bindings/misc/gpio-switch.txt
> >
> > diff --git a/Documentation/devicetree/bindings/misc/gpio-switch.txt b/Documentation/devicetree/bindings/misc/gpio-switch.txt
> > new file mode 100644
> > index 0000000..13528bd
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/misc/gpio-switch.txt
> > @@ -0,0 +1,47 @@
> > +Device-Tree bindings for gpio attached switches.
> > +
> > +This provides a mechanism to provide a named link to specified gpios. This can
> > +be useful in instances such as when theres a need to monitor a switch, which is
> > +common across a family of devices, but attached to different gpios and even
> > +implemented in different ways on differnet devices.
> > +
> > +Required properties:
> > +	- compatible = "gpio-switch";
> > +
> > +Each signal is represented as a sub-node of "gpio-switch". The naming of
> > +sub-nodes is arbitrary.
> > +
> > +Required sub-node properties:
> > +
> > +	- label: Name to be given to gpio switch.
> > +	- gpios: OF device-tree gpio specification.
> > +
> > +Optional sub-node properties:
> > +
> > +	- read-only: Boolean flag to mark the gpio as read-only, i.e. the line
> > +	  should not be driven by the host.
>
> In terms a a switch use, allowing driving it would be an override of the
> switch. Is that the idea here?

Yeah - since it had become a lot more generic and a lot of 
switches/signals would probably be implemented with a pull-up resistor 
of something like that, it seemed to make sense to allow them to be 
driven as well.

> > +
> > +Example nodes:
> > +
> > +        gpio-switch {
> > +                compatible = "gpio-switch";
>
> Both from a binding and driver perspective, there is no point in
> grouping these. Each node can simply have this compatible string.

True. I did it this way as this is how gpio-keys is implemented. OK, 
that has one optional parameter (autorepeat) for the block and this has 
none. Though I can also see that these probably have less in common than 
the individual lines used in gpio-keys.

> > +
> > +                write-protect {
> > +                        label = "write-protect";
> > +                        gpios = <&gpx3 0 GPIO_ACTIVE_LOW>;
> > +                        read-only;
> > +                };
> > +
> > +                developer-switch {
> > +                        label = "developer-switch";
> > +                        gpios = <&gpx1 3 GPIO_ACTIVE_HIGH>;
> > +                        read-only;
> > +                };
> > +
> > +                recovery-switch {
> > +                        label = "recovery-switch";
> > +                        gpios = <&gpx0 7 GPIO_ACTIVE_LOW>;
> > +                        read-only;
> > +                };
> > +        };
> > +
> > --
> > 2.1.4
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