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. Thanks, Mike -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
