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

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Date:   Tue, 24 Oct 2017 07:51:01 +0200
From:   Cédric Le Goater <clg@...d.org>
To:     Andrea Scian - DAVE Embedded Systems <andrea.scian@...e.eu>
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>,
        Andrew Jeffery <andrew@...id.au>
Subject: Re: about pca955x led driver gpio management

On 10/17/2017 11:16 AM, Andrea Scian - DAVE Embedded Systems wrote:
> 
>> 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.

Sorry I got distracted.

> 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)

euh ? what do you mean. There is a real system using this device tree. 
I think we would know about it if it didn't work. Please explain

> 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)

Please send the patch to discuss, add Andrew Jeffery <andrew@...id.au> 
in cc:

Thanks,

C.


> 
> 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,
>>>>>
>>>
>>