linux-kernel - Re: [PATCH] leds: pca9532: Extend pca9532 device tree support

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Date:   Thu, 9 Feb 2017 09:41:19 +0100
From:   Felix Brack <fb@...c.ch>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>, riku.voipio@....fi,
        rpurdie@...ys.net, pavel@....cz, linux-leds@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     f.brack@...s.ch
Subject: Re: [PATCH] leds: pca9532: Extend pca9532 device tree support

Hello Jacek,

On 08.02.2017 20:42, Jacek Anaszewski wrote:
> Hi Felix,
> 
> On 02/08/2017 05:12 PM, Felix Brack wrote:
>> Hello Jacek,
>>
>> On 07.02.2017 21:45, Jacek Anaszewski wrote:
>>> Hi Felix,
>>>
>>> Thanks for the patch.
>>>
>>> On 02/07/2017 07:11 PM, Felix Brack wrote:
>>>> This patch extends the device tree support for the pca9532 allowing LEDs to blink, dim or even being unchanged, i.e. not being turned off during driver initialization.
>>>
>>> Isn't it possible to apply desired settings with existing LED subsystem
>>> brightness file, and delay_on/off files exposed by timer trigger?
>>>
>>> Best regards,
>>> Jacek Anaszewski
>>>
>>
>> This might be a misunderstanding. My patch is not meant to replace
>> anything for driving the LEDs once the kernel is fully loaded. The LED
>> subsystem offers quite a lot of possibilities to do this.
>>
>> My patch mainly deals with the 'default' state of the LEDs immediately
>> when the driver gets loaded.
>> Here is an example: I have a system with a LED named 'RUN' which is
>> turned on steady by U-Boot (indicating "system booting"). When the
>> PCA9532 driver loads this LED gets turned off due to initialization.
>> However I would like it remain lit until later a script will make that
>> 'RUN' LED blink (indicating "system running"). This script will of
>> course use the existing LED subsystem to do so. To keep the 'RUN' LED
>> lit I need the DT property 'default-state' being set to 'PCA9532_KEEP'.
> 
> It looks like all you need is default-state property.

For the example with keeping the 'RUN' led turned on, yes. However I
would have to configure PSC and PWM registers to make the 'RUN' LED
blink, for example.

> I'd rather avoid exposing prescaler and pwm registers in DT.

I don't see that exposing PSC and PWM registers to the DT would do any
harm. Is there something I'm missing here?

> 

One could pass parameters to the driver but I think that is worse, as
nowadays we have DT.

regards Felix