linux-kernel - about pca955x led driver gpio management

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Date:   Tue, 17 Oct 2017 09:36:07 +0200
From:   Andrea Scian - DAVE Embedded Systems <andrea.scian@...e.eu>
To:     Cédric Le Goater <clg@...d.org>
Cc:     Bryan Wu <cooloney@...il.com>, Richard Purdie <rpurdie@...ys.net>,
        Jacek Anaszewski <j.anaszewski@...sung.com>,
        linux-leds@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: about pca955x led driver gpio management

Dear all,

I'm working on an iMX6 based board with a PCA9555 which is used both to 
drive LEDs and manage some GPIOs.

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@...-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@...-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,

-- 


Andrea SCIAN



*DAVE Embedded Systems*

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