Re: [PATCH v5 2/4] gpiolib: Add ability to get GPIO direction

Alan Cox
2011-03-08T12:14:28Z

> I don't object to a callback hook. My objection is how it is bodged
> on to work around limitations to the direction being cached in the
> flags variable. I want to see a solution that either depends entirely
> on the callback, or completely fixes the problems with the cached
> value by allowing the driver to update it.

Doing it all by callback might actually fix a lot of the problems because
it can handle all kinds of 'unknowns'. If the callbacks for set/get
optionally pass a char buffer as well even the /proc interface just comes
out in the wash as the device can return a string to populate the status
or to be parsed (obviously with most h/w using the default method which
is in/out)

However who then does the enforcement of gpio_foo calls if the flag is
not cached, does that end up in each driver or is there still a cache of
some form ?

Not sure updating the interface is that hard either - we've done it
before with other layers simply by starting off with

if (foo->ops->method)
foo->ops->method(foo, bar);
else {
old fixed method + glue
}

(or by forcing foo->ops->method on init to point to a default handler,
but that breaks making ops const)

Alan