On Fri, Sep 27, 2013 at 06:35:31AM -0700, Mike Dunn wrote: > On 09/26/2013 05:50 AM, Thierry Reding wrote: > > On Thu, Sep 26, 2013 at 03:26:13PM +0300, Tomi Valkeinen wrote: > >> On 26/09/13 15:02, Thierry Reding wrote: > >>> On Thu, Sep 26, 2013 at 01:13:18PM +0300, Tomi Valkeinen wrote: > >>>> On 11/09/13 14:40, Mike Dunn wrote: > >>>>> On 09/10/2013 10:21 AM, Thierry Reding wrote: > >>>> > >>>>>> Do you have a real setup that actually needs multiple GPIOs? Usually > >>>>>> such a setup requires some kind of timing or other additional > >>>>>> constraint > >>>>>> which can't be represented by this simple binding. > >>>>>> > >>>>>> Looking at the Palm Treo code it seems like the reason why multiple > >>>>>> GPIOs are needed is because one is to enable the backlight, while the > >>>>>> other is in fact used to enable the LCD panel. > >>>>> > >>>>> > >>>>> There are actually four GPIOs involved! (There is an embarrasingly > >>>>> horrible > >>>>> hack in arch/arm/mach-pxa/palmtreo.c that handles the others.) One is > >>>>> almost > >>>>> certainly simply backlight power. The other three are probably LCD > >>>>> related. > >>>> > >>>> When you say "power", do you mean the gpio enables a regulator to feed > >>>> power to the backlight? If so, wouldn't that be a regulator, not gpio, > >>>> from the bl driver's point of view? > >>>> > >>>> Generally speaking, this same problem appears in many places, but for > >>>> some reason especially in display. I'm a bit hesitant in adding "free > >>>> form" gpio/regulator support for drivers, as, as Thierry pointed out, > >>>> there are often timing requirements, or sometimes the gpios are > >>>> inverted, or sometimes the gpio is, in fact, a reset gpio, where you'll > >>>> assert the gpio for a short moment only. > >>> > >>> I sent out another series a few days ago that somewhat obsoletes this > >>> patch. What it does is basically add a single enable GPIO that can be > >>> used to turn the backlight on and off. In a separate patch, support is > >>> added for a power regulator. The combination of both should be able to > >>> cover the majority of use-cases. > >> > >> But Mike's case required 4 GPIOs? Or can that be reduced to one gpio and > >> one regulator? > > > > Well, at least for the backlight it only seemed to involve a single > > GPIO. The other three were probably related to LCD and therefore not > > really suitable for a backlight driver. Traditionally it has been that > > the backlight driver handled these things as well (via the callbacks > > installed by board setup code). While really they should be handled by a > > separate driver (for the LCD). > > > Yes, this is currently my best guess. This is reverse-engineered and > unfortunately I'm not yet able to accurately describe my particular use-case. > Probably as wacky as anything you can imagine, Thierry :) > > The gpio and regulator patches will probably suffice. Thierry, can you please > point me to those patches? I don't see them in your gitorious tree. If they > were posted to linux-pwm, I missed them; sorry.
I've stumbled across this email and it's not marked as answered, so here
goes: these patches will be part of my pull request for 3.13. They
should now be in my tree, although that's now moved to kernel.org. You
can find it here:
https://git.kernel.org/cgit/linux/kernel/git/thierry.reding/linux-pwm.git
Thierry
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