From mboxrd@z Thu Jan 1 00:00:00 1970 From: jg1.han@samsung.com (Jingoo Han) Date: Fri, 01 Nov 2013 08:37:23 +0900 Subject: [PATCHv4] video: backlight: gpio-backlight: Add DT support. In-Reply-To: <20131022200141.GA8037@mithrandir> 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> Message-ID: <001e01ced692$267a6d90$736f48b0$%han@samsung.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.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-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 > > > > > Cc: Jingoo Han > > > > > Cc: Laurent Pinchart > > > > > Cc: Rob Herring > > > > > Cc: Pawel Moll > > > > > Cc: Mark Rutland > > > > > Cc: Stephen Warren > > > > > Cc: Ian Campbell > > > > > Cc: devicetree at vger.kernel.org > > > > > Cc: Sascha Hauer > > > > > Cc: linux-arm-kernel at lists.infradead.org > > > > > Cc: Lothar Wa?mann > > > > > Cc: Jean-Christophe Plagniol-Villard > > > > > Cc: Eric B?nard > > > > > Signed-off-by: Denis Carikli > > > > > --- > > > > > 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