linux-kernel - Re: [PATCH] backlight: l4f00242t03: Fix reset sequence

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Date:	Wed, 05 Jan 2011 01:32:55 +0100
From:	Alberto Panizzo <maramaopercheseimorto@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Richard Purdie <rpurdie@...ys.net>,
	Marek Vasut <marek.vasut@...il.com>, Tejun Heo <tj@...nel.org>,
	Axel Lin <axel.lin@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] backlight: l4f00242t03: Fix reset sequence

On Tue, 2011-01-04 at 15:59 -0800, Andrew Morton wrote:
> On Sun, 28 Nov 2010 18:13:53 +0100
> Alberto Panizzo <maramaopercheseimorto@...il.com> wrote:
> 
> > The reset command is part of the init sequence and it take effect
> > only if the lcd is powered.
> > 
> > Signed-off-by: Alberto Panizzo <maramaopercheseimorto@...il.com>
> > ---
> > 
> > This patch is built on top of:
> > http://userweb.kernel.org/~akpm/mmotm/broken-out/drivers-video-backlight-l4f00242t03c-full-implement-fb-power-states-for-this-lcd.patch
> > 
> >  drivers/video/backlight/l4f00242t03.c |    3 ++-
> >  1 files changed, 2 insertions(+), 1 deletions(-)
> > 
> > diff --git a/drivers/video/backlight/l4f00242t03.c b/drivers/video/backlight/l4f00242t03.c
> > index 5d25743..c04aa90 100644
> > --- a/drivers/video/backlight/l4f00242t03.c
> > +++ b/drivers/video/backlight/l4f00242t03.c
> > @@ -62,6 +62,8 @@ static void l4f00242t03_lcd_init(struct spi_device *spi)
> >  		regulator_enable(priv->core_reg);
> >  	}
> >  
> > +	l4f00242t03_reset(pdata->reset_gpio);
> > +
> >  	gpio_set_value(pdata->data_enable_gpio, 1);
> >  	msleep(60);
> >  	spi_write(spi, (const u8 *)cmd, ARRAY_SIZE(cmd) * sizeof(u16));
> > @@ -225,7 +227,6 @@ static int __devinit l4f00242t03_probe(struct spi_device *spi)
> >  	}
> >  
> >  	/* Init the LCD */
> > -	l4f00242t03_reset(pdata->reset_gpio);
> >  	l4f00242t03_lcd_init(spi);
> >  	priv->lcd_state = FB_BLANK_VSYNC_SUSPEND;
> >  	l4f00242t03_lcd_power_set(priv->ld, FB_BLANK_UNBLANK);
> 
> What were the user-visible effects of the bug which you just fixed?
> 
> Please always include this info when sending a bugfix!  Because without
> that info it's much harder to work out whether we should backport the
> fix into earlier kernels and it's harder for end-users and distro
> maintainers to work out if the patch will fix particular behaviour
> which they or their customers are seeing.
> 

The effect of the bug was that the sequence:
set lcd power_state to FB_BLANK_POWERDOWN
set lcd power_state to FB_BLANK_UNBLANK
Did not produced a complete reboot of the LCD which was showing fuzzy 
colours.

This was not experienced before implementing correctly all the LCD power
states with the patch [1]. Since before the patch [1] the regulators
were not touched and the LCD shutdown was reached with a register 
write. After the patch [1] a complete boot sequence with an initial 
reset is needed for the display every time the LCD is powered up.

drivers-video-backlight-l4f00242t03c-full-implement-fb-power-states-for-this-lcd.patch

Best Regards,
-- 
Alberto!

        Be Persistent!
                - Greg Kroah-Hartman (FOSDEM 2010)

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