Hi guys,
I'm a little perplexed as to how I would define a GPIO
controller in a device tree but mark off pins as available or
not, so users can geek around in their own drivers without
defining in a device tree exactly what they intend to use it
for (especially if it's something really weird).
Easiest example - the Efika runs an MPC5200B has 3 GPIO pins
on the board. It's not much, but they're there for use. All
the other GPIOs are absolutely out of bounds, off limits and
probably dangerous to touch, but since each GPIO block has a
32-bit register to handle them, you can twiddle any bit you
like with impunity and cause all the damage you want. A simple
thought comes to mind in that the gpiolib should not allow a
request for one of these "bad" GPIO pins to succeed.
So, how do we define in a bank of GPIOs, which ones are free
for use, without them being attached to a device and given as
a "gpios" property?
Would we suggest a node;
gpio-header {
compatible = "bplan,efika-gpio";
gpios = <&gpio-standard 16 0 17 0>;
};
gpio-header2 {
compatible = "bplan,efika-gpio-wkup";
gpios = <&gpio-wkup 18 0>;
};
Which a driver can then look for? I would much rather I did
not have to come up with a special compatible property though,
after all, MPC5200B GPIO are not special and the Efika does
not do fancy magic with them :)
My goal is basically to give an entry in the device tree
whereby (using a forth script) you can pick between IrDA,
GPIO, a Sleep Switch (for Sylvain's patch for Lite5200 and
Efika from a year or two ago..), or whatever else you like.
But a generic GPIO "geek port" is basically then undefined and
left hanging.
By the way I did notice that none of the GPT timer entries in
the lite5200b.dts have GPIO references and the GPT GPIO block
is not defined. Is this because the timers are not exposed on
the board for GPIO or just no need for it? Each timer has a
pin it can sample, drive and do PWM on.. this leads me to
wonder how the PWM driver framework as announced/proposed last
week would work here, and if the device tree should
specifically pick which operation works on which timer (after
all if you have a PWM fan controller on a timer pin, you would
want to advertise the fact, but having the full 8 timers as a
"gpio-controller" and "pwm-controller" both at the same time,
sharing the same reg property but supporting only a subset of
that controller, needs addressing.
--
Matt Sealey <[EMAIL PROTECTED]>
Genesi, Manager, Developer Relations
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