Re: [PATCH] pwm-backlight: Turn off pwm backlight in probe

[Markus Pargmann <mpa@pengutronix.de>]

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On Tue, Oct 07, 2014 at 02:47:53PM +0530, Ajay kumar wrote:
> On Tue, Oct 7, 2014 at 2:37 PM, Markus Pargmann <mpa@pengutronix.de> wrote:
> > Hi,
> >
> > On Tue, Oct 07, 2014 at 10:35:49AM +0200, 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.
> >
> > Yes your proposal looks a lot better to handle the different use cases.
> > The DT-binding is not a hardware description but I don't see any better
> > way of passing that information. So it would be good to get your
> > solution mainline.
> +1
> And, I have already tested Thierry's proposal on Exynos5800 peach_pi.

I also tested Thierry's patch on i.MX6s now and it works fine.

Regards,

Markus

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