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Date: Wed, 25 Jun 2014 11:59:10 -0300
From: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
To: "Gupta, Pekon" <pekon@ti.com>
Subject: Re: [PATCH v1 3/3] ARM: dts: am335x-bone: add support for beaglebone
 LCD4 cape
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Cc: Tony Lindgren <tony@atomide.com>, Jason Kridner <jkridner@gmail.com>,
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On 25 Jun 04:38 AM, Gupta, Pekon wrote:
> >From: Ezequiel Garcia
> >>On 24 Jun 05:54 PM, Pekon Gupta wrote:
> >> This patch adds support for LCD4 cape as advertised on
> >>   http://elinux.org/CircuitCo:BeagleBone_LCD4
> >>
> >> This cape has:
> >> * 480x272 TFT-LCD panel
> >>  - LCD panel datasheet and timing information are sourced from [1]
> >>  - LCD backlight is connected to 'EHRPWM1A' on cape board, but its used for
> >>    enabling backlight power-supply. So 'gpio-backlight' driver is used instead
> >>    of 'pwm-backlight' driver (Kconfig: BACKLIGHT_GPIO=y).
> >>
> >
> >I'm confused about this, can you clarify why you are not using pwm-backlight?
> >
> 
> As per the schematics of this LCD4 cape board, "EHRPWM1A" pin controls
> enabling/disabling of the power to backlight LED. It does not control the
> voltage levels (brightness levels) of the LED. Thus it wasn't making sense
> to use pwm-backlight driver which more suitable in cases where you have
> multiple levels of brightness.
> Here, you have only 2 levels "backlight=off | on", so I used gpio-backlight driver.
> Though you can use pwm-backlight driver also, but the backlight turns ON
> only when you set the /sys/class/backlight/<backlight_device>/brighteness
> to maximum level (as set in DT).
> 

Hm, I didn't know that. Thanks for this information.
-- 
Ezequiel Garcia, VanguardiaSur
www.vanguardiasur.com.ar