linux-kernel - Re: about pca955x led driver gpio management

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Message-ID: <4ac527f2-c59e-70a2-efd4-da52370ea557@dave.eu>
Date:   Tue, 17 Oct 2017 11:16:59 +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: Re: about pca955x led driver gpio management


> 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@...-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,
>>>>
>>
> 

View attachment "0001-leds-pca955x-map-gpio-offset-to-led-index-correctly.patch" of type "text/plain" (3422 bytes)