Re: [PATCH] leds: pca955x: add GPIO support

[Pavel Machek <pavel@ucw.cz>]

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Hi!

> > On Tue 2017-05-09 08:36:12, Cédric Le Goater wrote:
> >> The PCA955x family of chips are I2C LED blinkers whose pins not used
> >> to control LEDs can be used as general purpose I/Os (GPIOs).
> >>
> >> The following adds support for device tree and Open Firmware to be
> >> able do define different operation modes for each pin. See bindings
> >> documentation for more details. The pca955x driver is then extended
> >> with a gpio_chip when pins are operating in GPIO mode.
> > 
> > Actually.. maybe better solution would be to turn this into GPIO
> > driver, and then use gpio-leds on top...?
> 
> yes probably. We could introduce a new driver for the PCA955[0-3]
> when all pins are in GPIO mode. I have taken the approach of the 
> leds-pca9532 which behaves quite similarly.

Does the GPIO mode differ electrically?

> > What is the difference between pin in GPIO mode and pin in LED mode?
> 
> Well, first of all the PCA955[0-3] are LED blinkers chips, and not 
> GPIO chips. So you have an extra couple registers to set the frequency 
> and the pwm.

Well.. PWM is used all over the place, not only for LEDs.

> As for the pins in GPIO mode, here is what the specs says : 
> 
> - For input, set LEDn to high-impedance (01) and then read the pin 
>   state via the input register.
> 
> - For output, LED output pin is HIGH when the output is programmed 
>   as high-impedance, and LOW when the output is programmed LOW through 
>   the LS register. The output can also be pulse-width controlled when 
>   PWM0 or PWM1 are used.
> 
> So for output, GPIO control is quite similar to LED control. For input,
> the INPUTx registers need to be read.

Ok, makes sense. So you have GPIO pins with PWM support. (And some
kind of blinking? Blinking sounds like a low frequency PWM to me :-).

Can you take a look at drivers/pwm?

Thanks,
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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