linux-kernel - RE: [PATCH 0/3] LP3943 MFD driver for a GPIO expander and a PWM generator

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Message-ID: <A874F61F95741C4A9BA573A70FE3998F82E83168@DQHE06.ent.ti.com>
Date:	Mon, 22 Jul 2013 01:19:10 +0000
From:	"Kim, Milo" <Milo.Kim@...com>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	"sameo@...ux.intel.com" <sameo@...ux.intel.com>,
	"lee.jones@...aro.org" <lee.jones@...aro.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"thierry.reding@...il.com" <thierry.reding@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>
Subject: RE: [PATCH 0/3] LP3943 MFD driver for a GPIO expander and a PWM
 generator

Hi Linus,
Thanks for your review.

> On Tue, Jul 16, 2013 at 4:38 AM, Kim, Milo <Milo.Kim@...com> wrote:
> 
> > LP3943 is an integrated device capable of driving 16 output channels.
> > It supports a GPIO expander and a PWM generator.
> 
> But actually the data sheet describes it as a LED driver with PWM
> chip.
> 
> Do you have use cases not using it for LEDs but other thing or why
> do you want to model the 16 LED lines as GPIO lines?
> Why can't you just have a drivers/leds/* as for any other LED
> chip?

We have two ways to provide LED functions.

(a) Creating LP3943 LED driver.
This is what you mentioned.
LP3943 MFD will consist of GPIO, LED and PWM drivers

(b) Using a LED PWM driver with the PWM generator
With LP3943 PWM driver, we can control LEDs by using LED PWM driver
under drivers/leds/leds-pwm.c
Then, the MFD consists of just two drivers - GPIO and PWM.
LP3943 PWM driver can be used as general usages -
Not only simple LED drivers but also the PWM signal input for a backlight device.
That's why I prefer to the second way.

> Atleast some good explanation of this needs to be found in the
> patch text and also as comments in Kconfig and the code I think.

I should describe the usage of the 'leds-pwm' driver for LED lighting.
Thanks for this guideline.

Regards,
Milo
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