[PATCHv4] video: backlight: gpio-backlight: Add DT support.

[Jingoo Han]

On Wednesday, October 23, 2013 5:02 AM, Thierry Reding wrote:
> On Tue, Oct 22, 2013 at 05:34:45PM +0200, Jean-Christophe PLAGNIOL-VILLARD wrote:
> > On 09:23 Tue 22 Oct     , Thierry Reding wrote:
> > > On Tue, Oct 22, 2013 at 06:58:33AM +0200, Jean-Christophe PLAGNIOL-VILLARD wrote:
> > > > On 11:13 Mon 21 Oct     , Denis Carikli wrote:
> > > > > Cc: Richard Purdie <rpurdie at rpsys.net>
> > > > > Cc: Jingoo Han <jg1.han at samsung.com>
> > > > > Cc: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > > > > Cc: Rob Herring <rob.herring at calxeda.com>
> > > > > Cc: Pawel Moll <pawel.moll at arm.com>
> > > > > Cc: Mark Rutland <mark.rutland at arm.com>
> > > > > Cc: Stephen Warren <swarren at wwwdotorg.org>
> > > > > Cc: Ian Campbell <ijc+devicetree at hellion.org.uk>
> > > > > Cc: devicetree at vger.kernel.org
> > > > > Cc: Sascha Hauer <kernel at pengutronix.de>
> > > > > Cc: linux-arm-kernel at lists.infradead.org
> > > > > Cc: Lothar Waßmann <LW at KARO-electronics.de>
> > > > > Cc: Jean-Christophe Plagniol-Villard <plagnioj at jcrosoft.com>
> > > > > Cc: Eric Bénard <eric at eukrea.com>
> > > > > Signed-off-by: Denis Carikli <denis at eukrea.com>
> > > > > ---
> > > > > ChangeLog v3->v4:
> > > > > - The default-brightness property is now optional, it defaults to 1 if not set.
> > > > by default we set OFF not ON
> > > >
> > > > do not actiate driver or properti by default you can not known to consequence
> > > > on the hw
> > >
> > > Turning on a backlight by default is what pretty much every backlight
> > > driver does. I personally think that's the wrong default, I even tried
> > > to get some discussion started recently about how we could change this.
> > > However, given that this has been the case for possibly as long as the
> > > subsystem has existed, suddenly changing it might cause quite a few of
> > > our users to boot the new kernel and not see their display come up. As
> > > with any other ABI, this isn't something we can just change without a
> > > very good migration path.
> >
> > I'm sorry but the blacklight descibe in DT have nothing to do with the common
> > pratice that the current driver have today
> 
> That's not at all what I said. What I said was that the majority of
> backlight drivers currently default to turning the backlight on when
> probed. Therefore I think it would be consistent if this driver did the
> same.
> 
> I also said that I don't think it's a very good default, but at the same
> time we can't just go and change the default behaviour at will because
> people may rely on it.

I agree with your opinion.
But, I can't decide how to change it.

> 
> > put on by default if wrong specially without the property define. Even put it
> > on by default it wrong as the bootloader may have set it already for splash
> > screen and to avoid glitch the drivers need to detect this.
> 
> I agree that would be preferable, but I don't know of any way to detect
> what value the bootloader set a GPIO to. The GPIO API requires that you
> call gpio_direction_output(), and that requires a value parameter which
> will be used as the output level of the GPIO.

Jean-Christophe's point is right.

We may need to discuss 'the way to detect what value the bootloader
set a GPIO to'.

> > For me this should not even be a property but handled by the driver them
> > selves in C.
> 
> Agreed. There has been some discussion recently about whether devicetree
> should be extended (or supplemented) to allow defining behaviour as well
> (in addition to just hardware). But that's not immediately relevant here
> at this time.

Agreed.

Best regards,
Jingoo Han