From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jingoo Han Subject: Re: [PATCHv4] video: backlight: gpio-backlight: Add DT support. Date: Fri, 01 Nov 2013 08:37:23 +0900 Message-ID: <001e01ced692$267a6d90$736f48b0$%han@samsung.com> References: <20131019104555.GI18477@ns203013.ovh.net> <1382346813-8449-1-git-send-email-denis@eukrea.com> <20131022045833.GB17512@ns203013.ovh.net> <20131022072307.GA8681@ulmo.nvidia.com> <20131022153445.GD17512@ns203013.ovh.net> <20131022200141.GA8037@mithrandir> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-reply-to: <20131022200141.GA8037@mithrandir> Content-language: ko Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: 'Thierry Reding' , 'Jean-Christophe PLAGNIOL-VILLARD' Cc: 'Denis Carikli' , 'Mark Rutland' , devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, 'Ian Campbell' , 'Eric B??nard' , 'Pawel Moll' , 'Stephen Warren' , 'Rob Herring' , 'Richard Purdie' , 'Laurent Pinchart' , 'Sascha Hauer' , linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, 'Lothar Wa??mann' , 'Jingoo Han' List-Id: devicetree@vger.kernel.org On Wednesday, October 23, 2013 5:02 AM, Thierry Reding wrote: > On Tue, Oct 22, 2013 at 05:34:45PM +0200, Jean-Christophe PLAGNIOL-VI= LLARD wrote: > > On 09:23 Tue 22 Oct , Thierry Reding wrote: > > > On Tue, Oct 22, 2013 at 06:58:33AM +0200, Jean-Christophe PLAGNIO= L-VILLARD wrote: > > > > On 11:13 Mon 21 Oct , Denis Carikli wrote: > > > > > Cc: Richard Purdie > > > > > Cc: Jingoo Han > > > > > Cc: Laurent Pinchart > > > > > Cc: Rob Herring > > > > > Cc: Pawel Moll > > > > > Cc: Mark Rutland > > > > > Cc: Stephen Warren > > > > > Cc: Ian Campbell > > > > > Cc: devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org > > > > > Cc: Sascha Hauer > > > > > Cc: linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org > > > > > Cc: Lothar Wa=C3=9Fmann > > > > > Cc: Jean-Christophe Plagniol-Villard > > > > > Cc: Eric B=C3=A9nard > > > > > Signed-off-by: Denis Carikli > > > > > --- > > > > > ChangeLog v3->v4: > > > > > - The default-brightness property is now optional, it default= s 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 backl= ight > > > 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 a= s the > > > subsystem has existed, suddenly changing it might cause quite a f= ew of > > > our users to boot the new kernel and not see their display come u= p. As > > > with any other ABI, this isn't something we can just change witho= ut 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 >=20 > 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 t= he > same. >=20 > I also said that I don't think it's a very good default, but at the s= ame > time we can't just go and change the default behaviour at will becaus= e > people may rely on it. I agree with your opinion. But, I can't decide how to change it. >=20 > > put on by default if wrong specially without the property define. E= ven put it > > on by default it wrong as the bootloader may have set it already fo= r splash > > screen and to avoid glitch the drivers need to detect this. >=20 > I agree that would be preferable, but I don't know of any way to dete= ct > what value the bootloader set a GPIO to. The GPIO API requires that y= ou > call gpio_direction_output(), and that requires a value parameter whi= ch > 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. >=20 > Agreed. There has been some discussion recently about whether devicet= ree > should be extended (or supplemented) to allow defining behaviour as w= ell > (in addition to just hardware). But that's not immediately relevant h= ere > at this time. Agreed. Best regards, Jingoo Han -- To unsubscribe from this list: send the line "unsubscribe devicetree" i= n the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html