Re: about pca955x led driver gpio management

[Andrea Scian - DAVE Embedded Systems]

This is a multi-part message in MIME format.
> On 10/17/2017 10:20 AM, Andrea Scian - DAVE Embedded Systems wrote:
> > Il 17/10/2017 10:18, Cédric Le Goater ha scritto:
> > > On 10/17/2017 09:36 AM, Andrea Scian - DAVE Embedded Systems wrote:
> > > > Dear all,
> > > >
> > > > I'm working on an iMX6 based board with a PCA9555 which is used both to drive LEDs and manage some GPIOs.
> > > The PCA9555 chip and the PCA955[0-3] chips have different control
> > > registers. You need a different led driver for it.
> >
> > My typo sorry, as you can see in the device tree below, I'm using pca9551
>
> ok.
>
> You might want to take a look at how we mixed gpios and leds on the witherspoon
> system using pca9552 chips. we added a gpio-leds binding.
>
> https://github.com/openbmc/linux/blob/dev-4.10/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts

understood: you configure all pins of PCA955x as GPIOs and the map the 
one you need as led with gpio-leds binding.

However to me this is a kind of workaround or, at least, there's nothing 
about this limitation into the devicetree binding (in fact, IMHO, the 
device tree binding example will just fail)

I wrote the attached patch which should fix the issue and allow a more 
generic approach. WDYT?

(in case it looks good, I'll send the patch in the correct way)


Kind Regards,

Andrea

> > > > My current kernel is quite old (4.1.15) but I've found Cédric patches on mainline and backported to this old revision.
> > > >
> > > > I'm facing an issue with it, because it seems that it fails when it's used in a mixed (led/gpios) environment.
> > > >
> > > > E.g.: let's say that I have one led connected to LED0 output and one GPIO connected at LED1 output.
> > > >
> > > > I define it as
> > > >
> > > >                           pca9551: pca9551@60 {
> > > >                                   compatible = "nxp,pca9551";
> > > >                                   reg = <0x60>;
> > > >                                   #address-cells = <1>;
> > > >                                   #size-cells = <0>;
> > > >                                   #gpio-cells = <1>;
> > > >
> > > >                                   led@0 {
> > > >                                           label = "led0";
> > > >                                           reg = <0>;
> > > >                                           linux,default-trigger = "none";
> > > >                                   };
> > > >                                   gpio@1 {
> > > >                                           label = "gpio1";
> > > >                                           reg = <1>;
> > > >                                           type = <2>; /* GPIO */
> > > >                                   };
> > > >                   };
> > > >
> > > > At boot it's probed as
> > > >
> > > > root@sbc-lynx:~# dmesg | grep pca
> > > > [    5.315425] leds-pca955x 5-0060: leds-pca955x: Using pca9551 8-bit LED driver at slave address 0x60
> > > > [    5.350349] leds-pca955x 5-0060: gpios 511...511
> > > >
> > > > But I cannot access it:
> > > >
> > > > root@sbc-lynx:~# echo 511 > /sys/class/gpio/export
> > > > -sh: echo: write error: Device or resource busy
> > > >
> > > > Because for pca955x_gpio_request_pin() this is at offset 0 (in fact is the first gpio registered of this gpio_chip) but it's the index 1 inside pca955x->leds[]
> > > >
> > > > Am I missing something? (maybe I made a mistake in my backport and/or I'm missing some patches about the GPIO subsystems).
> > > >
> > > > If I'm right I think I can send a patch to fix this (I'm thinking about having an array of GPIO index to map offset -> pca955x->leds[] index or just register all pins as GPIOs and then just report the busy state)
> > > >
> > > > WDYT?
> > > >
> > > > Kind Regards,