[PATCH] ARM: mxs/tx28: fix up LCD pads

[Lothar Waßmann]

Hi,

Shawn Guo writes:
> On Fri, Mar 11, 2011 at 05:16:18PM +0100, Lothar Waßmann wrote:
> > Hi,
> > 
> > Shawn Guo writes:
> > > * In any case, LCD only needs one group of VSYNC, HSYNC, and DOTCLK.
> > >   So remove the redundant and useless one.
> > > * LCD_ENABLE pad should not work as a GPIO for LCD, and there must be
> > >   one pad for ENABLE function.
> > > 
> > > Signed-off-by: Shawn Guo <shawn.guo at freescale.com>
> > > ---
> > > Hi Lothar, Uwe,
> > > 
> > > I do not have the schematics of TX28 board, and I'm guessing the fix.
> > > So it really needs your comments here.
> > > 
> > > Regards,
> > > Shawn
> > > 
> > >  arch/arm/mach-mxs/mach-tx28.c |    6 +-----
> > >  1 files changed, 1 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/arch/arm/mach-mxs/mach-tx28.c b/arch/arm/mach-mxs/mach-tx28.c
> > > index b65e371..16a0059 100644
> > > --- a/arch/arm/mach-mxs/mach-tx28.c
> > > +++ b/arch/arm/mach-mxs/mach-tx28.c
> > > @@ -61,11 +61,7 @@ static const iomux_cfg_t tx28_stk5v3_pads[] __initconst = {
> > >  	MX28_PAD_LCD_RD_E__LCD_VSYNC | LCD_MODE,
> > >  	MX28_PAD_LCD_WR_RWN__LCD_HSYNC | LCD_MODE,
> > >  	MX28_PAD_LCD_RS__LCD_DOTCLK | LCD_MODE,
> > > -	MX28_PAD_LCD_CS__LCD_CS | LCD_MODE,
> > >
> > This one is correct as it stands (i.e. the suggested change is wrong).
> > 
> So your panel is using LCD_CS without using LCD_RS as a couple?
> 
Sorry, I confused LCD_CS and LCD_ENABLE. It doesn't use LCD_CS, but
the LCD_ENABLE function on the LCD_CS pad. Thus, the pad should be
configured as:
MX28_PAD_LCD_CS__LCD_ENABLE | LCD_MODE,

> > > -	MX28_PAD_LCD_VSYNC__LCD_VSYNC | LCD_MODE,
> > > -	MX28_PAD_LCD_HSYNC__LCD_HSYNC | LCD_MODE,
> > > -	MX28_PAD_LCD_DOTCLK__LCD_DOTCLK | LCD_MODE,
> > >
> > These should be removed from the pin list, as suggested.
> > 
> > > -	MX28_PAD_LCD_ENABLE__GPIO_1_31 | LCD_MODE,
> > > +	MX28_PAD_LCD_CS__LCD_ENABLE | LCD_MODE,
> > >
> > This change is also wrong. The pad is used as a (power) enable pin for
> > a certain family of LCDs that we recommend for use with our
> > modules. It should be configured as GPIO and pulled high/low whenever
> > the LCD is activated/deactivated (just like the LCD_RESET pad below).
> > 
> This pad is not designed for a power enable pin but DATA_ENABLE
>
It's also designed to be used as a GPIO, which is what we are doing.

> signal.  Why does your panel need two power enable pins here, LCD_CS
> and LCD_RESET?
> 
You should ask the manufacturer of the LCD panel. As far as I can tell
asserting LCD_RESET stops the LCD controller, while the pin connected
to the LCD_ENABLE pad enables the backlight (which can be controlled
further via a PWM input).


Lothar Waßmann
-- 
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