linux-kernel - Re: [PATCH v6 2/2] leds: lm3601x: Introduce the lm3601x LED driver

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Date:   Thu, 17 May 2018 23:26:45 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Dan Murphy <dmurphy@...com>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Pavel Machek <pavel@....cz>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>
Subject: Re: [PATCH v6 2/2] leds: lm3601x: Introduce the lm3601x LED driver

Dan,

On 05/17/2018 04:34 PM, Dan Murphy wrote:
> Jacek
> 
> On 05/16/2018 04:17 PM, Dan Murphy wrote:
> <snip>
> 
>>>>>
>>>>>
>>>>>>>> +               if (!ret)
>>>>>>>
>>>>>>> if (ret) sounds more natural. And better just to split
>>>>>>>
>>>>>>>> +                       snprintf(led->led_name, sizeof(led->led_name),
>>>>>>>> +                               "%s:%s", led->led_node->name, name);
>>>>>>>> +               else
>>>>>>>> +                       snprintf(led->led_name, sizeof(led->led_name),
>>>>>>>> +                               "%s:torch", led->led_node->name);
>>>>>>>
>>>>>>> const char *tmp;
>>>>>>>
>>>>>>> ret = device_property_read_...(&tmp);
>>>>>>> if (ret)
>>>>>>>    tmp = ...
>>>>>>> sprintf(...);
>>>>
>>>> We're no longer taking devicename section of a LED class device name
>>>> from DT, so it will look differently anyway.
>>>>
> 
> So in adding the device_property code I think we again are reaching the LED label issue.
> In ARM with DT we would take the parent device node name and append it to the label

AFAIR this approach (parent DT node name used for devicename ) was 
incidentally applied in leds-as3645a.c. Soon after that we started
to use led-controller for parent DT name, according to Rob's request.

In the most of LED class drivers this is a child DT node which is used
for devicename, in case label is absent.

> if the optional label property was not available.  In migrating to the device_property
> APIs we don't or can't depend on that parent node anymore.
> 
> So for the case where the label property does not exist should we use a hard coded name
> or should we try to use the name from a device_id table.
> 
> This is how we did this for the leds-lp8860 driver.  If the label did not exist we used the
> i2c_device_id table and pulled the string from there.

i2c_device_id can't be applied as a generic pattern, but only for I2C
hooked devices. Nonetheless since it allows to save few lines of code
in case of drivers supporting a family of chips we can use it.

We are going to get rid of a devicename section from LED class device
name soon anyway, since it is redundant.

-- 
Best regards,
Jacek Anaszewski