On Tue, Oct 28, 2008 at 10:53 AM, Matt Sealey [off-list ref] wrote:

Is it still possible to perhaps create a node under lcd-controller which
describes the pin groupings? Maybe we should call it a gpio-group.

That way lcd-controller looks like

lcd-controller {
       compatible = "crystalfontz,something-gpio";
       data-bus {
               compatible - "gpio-group";
               gpios = <gpioc 1 gpioc 8 gpioc 42 ... >
       }
       rw-ctrl {
               compatible = "gpio-group";
               gpios = <gpioc 2>
       }

At this level, the 'compatible = "gpio-group";' is completely
irrelevant.  The binding for "crystalfontz,something-gpio" must
specify that there are two subnodes; one named data-bus and one named
rw-ctrl.  The driver, which binds against compatible in the parent
node, would know to go looking for those child nodes and to use the
gpios property inside them.  Simple.

quoted

Does this mean "hard-coding"?

No. If you have an array of GPIO pins (gpios property) then how do you
determine which is for data and which is some control pin? Do you
associate these numbers in the driver somehow? Maybe a matchlist or
an array? Given pins A B C D E F G H I J where does the data bus
start and the control pins live? A and B? A and J? I and J?

You know because you document it in the binding.

It would be definitely frivolous to define a whole device tree binding
for the *order in which you MUST specify the gpios for this particular
device*. There is obviously an implicit ordering of the GPIOs to make
up the data bus (you'd expect an order from MSB to LSB.. or perhaps
LSB to MSB... that might be better defined than undefined)

Why is it frivolous?  We do this all the time for reg and irqs.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.