From mboxrd@z Thu Jan  1 00:00:00 1970
From: lee.jones@linaro.org (Lee Jones)
Date: Tue, 7 Oct 2014 10:06:27 +0100
Subject: [PATCH] pwm-backlight: Turn off pwm backlight in probe
In-Reply-To: <20141007083548.GD24254@ulmo>
References: <1412623364-14583-1-git-send-email-mpa@pengutronix.de>
 <20141007083548.GD24254@ulmo>
Message-ID: <20141007090627.GH25331@lee--X1>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Tue, 07 Oct 2014, Thierry Reding wrote:

> On Mon, Oct 06, 2014 at 09:22:44PM +0200, Markus Pargmann wrote:
> > The backlight will be enabled by the panel again if it is used. So we
> > can save the default brightness and disable the pwm backlight when
> > probing.
> > 
> > Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
> > ---
> >  drivers/video/backlight/pwm_bl.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
> > index 336b83be7e2d..b4f433a6f106 100644
> > --- a/drivers/video/backlight/pwm_bl.c
> > +++ b/drivers/video/backlight/pwm_bl.c
> > @@ -317,9 +317,11 @@ static int pwm_backlight_probe(struct platform_device *pdev)
> >  		data->dft_brightness = data->max_brightness;
> >  	}
> >  
> > -	bl->props.brightness = data->dft_brightness;
> > +	bl->props.brightness = 0;
> >  	backlight_update_status(bl);
> >  
> > +	bl->props.brightness = data->dft_brightness;
> > +
> >  	platform_set_drvdata(pdev, bl);
> >  	return 0;
> >  
> 
> It would be nice if it was that easy. But we can't do this, because it
> will regress for users of this driver that don't use a panel or DRM. If
> the PWM backlight driver is used for example in conjunction with a plain
> fbdev driver it isn't necessarily hooked up with anything and won't be
> enabled automatically. That's really bad if fbdev is the only output you
> have since you'd have to blindly type the commands to enable the
> backlight. Furthermore disabling backlight isn't always what you want to
> do. For example if the bootloader already turned it on and you hand over
> from bootloader to kernel in a seamless way, then you absolutely want to
> keep backlight on all the time.
> 
> See also[0] for a different proposal to solve the same problem. Back at
> the time that received only a very few replies, but it would be nice if
> Lee and Bryan could look at it again and see if we can come up with some
> way to deal with this situation.

I don't have any experience with this stuff.  Jingoo and Bryan are the
_real_ reviewers for Backlight.  I just maintain the patches.  That
and I'm already swamped with MFD.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org ? Open source software for ARM SoCs
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