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

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Message-ID: <7aef407c-3b85-a18a-c19d-72545211a4cc@gmail.com>
Date:   Thu, 9 Feb 2017 22:10:21 +0100
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Felix Brack <fb@...c.ch>, 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

Hi Felix,

On 02/09/2017 09:41 AM, Felix Brack wrote:
> 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?

It is driver's responsibility to configure registers basing on user
settings. Let's stick to this scheme.

-- 
Best regards,
Jacek Anaszewski