Re: [PATCH 1/3] Device tree binding documentation for chromeos-firmware

[Martyn Welch]

On 03/12/15 15:08, Rob Herring wrote:
> On Thu, Dec 3, 2015 at 4:14 AM, Martyn Welch
> <martyn.welch@xxxxxxxxxxxxxxx> wrote:
> > On 02/12/15 15:15, Rob Herring wrote:
> > > On Tue, Dec 01, 2015 at 07:12:49PM +0000, Martyn Welch wrote:
> > > > This patch adds documentation for the chromeos-firmware binding.
> > > >
> > > > Cc: Rob Herring <robh+dt@xxxxxxxxxx>
> > > > Cc: Pawel Moll <pawel.moll@xxxxxxx>
> > > > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > > > Cc: Ian Campbell <ijc+devicetree@xxxxxxxxxxxxxx>
> > > > Cc: Kumar Gala <galak@xxxxxxxxxxxxxx>
> > > > Cc: devicetree@xxxxxxxxxxxxxxx
> > > > Signed-off-by: Martyn Welch <martyn.welch@xxxxxxxxxxxxxxx>
> > > > ---
> > > >    .../devicetree/bindings/misc/chromeos-firmware.txt | 27
> > > > ++++++++++++++++++++++
> > >
> > >
> > > bindings/firmware/ please.
> > >
> > > >    1 file changed, 27 insertions(+)
> > > >    create mode 100644
> > > > Documentation/devicetree/bindings/misc/chromeos-firmware.txt
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/misc/chromeos-firmware.txt
> > > > b/Documentation/devicetree/bindings/misc/chromeos-firmware.txt
> > > > new file mode 100644
> > > > index 0000000..8240611
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/misc/chromeos-firmware.txt
> > > > @@ -0,0 +1,27 @@
> >
> >
> > <snip>
> >
> > > > +
> > > > +Each signal is represented as a sub-node of "chromeos_firmware":
> > > > +Subnode properties:
> > > > +
> > > > +       - gpios: OF device-tree gpio specification.
> > > > +
> > > > +Example nodes:
> > > > +
> > > > +       chromeos_firmware {
> > >
> > >
> > > This should go under /firmware
> >
> > I've changed this to be:
> >
> >          firmware {
> >                  chromeos {
> >                          ...
> >                  };
> >          ];
> >
> > Which I generally accept (assuming this is considered a part of the
> > firmware) as a better way to represent this in the device tree, however this
> > has the nasty side effect of causing the device tree parsing to avoid
> > parsing the chromeos child and seeing it's compatible property (as the
> > firmware node isn't a bus), resulting in the probe routine not being called.
> >
> > If I add a 'compatible = "simple-bus"' property to the firmware node it
> > works, but this doesn't seem quite right as I believe "simple-bus" is
> > defined as a "simple memory mapped bus".
> >
> > I /could/ rewrite the initialisation to call of_find_compatible_node(), but
> > this seems rather hacky and inefficient. I can think of 2 other ways this
> > could be resolved:
> >
> > (1) As this is only tangentially related to firmware, I rename it something
> > like "chromeos-signals" and make it it's own node. In essence this driver
> > provides a mechanism built on top of specific GPIO (ala gpio-keys seems to
> > be, after-all this has a similar use of resources to that).
>
> I'm starting to fail to understand the relationship to firmware here...
>
> gpio-keys are at least a thing (being a key or set of keys). Your
> grouping is a rather random collection of GPIOs. Maybe you need
> "gpio-switch" binding and then the function would be "label" property.

So, something like this:

gpio-switch {
	compatible = "gpio-switch";

	pinctrl-names = "default";
	pinctrl-0 = <&wp_gpio &dev_mode &rec_mode>;

	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;
	};
};

(Making it much more generic in the process.)


> > (2) Add a compatible string something like 'compatible="logical-group";' to
> > the firmware node and add that too the bus matching logic. This would have
> > the advantage of solving this in the general case (I guess there are other
> > instances where a grouping of things more logically rather than physically
> > connected would ideally be grouped together), though I expect there may be
> > some strong views regarding this approach.
>
> Why do you need them grouped?

That's effectively what is achieved by putting this (and I assume 
anything else considered "firmware" under a firmware node isn't it? (or 
and I miss-understanding your request?)

I think it is a moot point, I'll rework as you've suggested.

Martyn
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