Re: [PATCH 1/2] gpio/crystalcove: Export Panel and backlight en/disable signals as GPIO

From: "Kumar, Shobhit" <shobhit.kumar@intel.com>
To: "linus.walleij@linaro.org" <linus.walleij@linaro.org>
Cc: "Lu, Aaron" <aaron.lu@intel.com>,
	"gnurou@gmail.com" <gnurou@gmail.com>,
	"Nikula, Jani" <jani.nikula@intel.com>,
	"intel-gfx@lists.freedesktop.org"
	<intel-gfx@lists.freedesktop.org>,
	"thierry.reding@gmail.com" <thierry.reding@gmail.com>,
	"lejun.zhu@linux.intel.com" <lejun.zhu@linux.intel.com>,
	"Vetter, Daniel" <daniel.vetter@intel.com>
Subject: Re: [PATCH 1/2] gpio/crystalcove: Export Panel and backlight en/disable signals as GPIO
Date: Fri, 6 Mar 2015 16:23:07 +0000	[thread overview]
Message-ID: <1425658984.2637.17.camel@intel.com> (raw)
In-Reply-To: <CACRpkdZcpftmzpmthwrOC2LK-4ck2PfT3tDP0Yc+eV9Qy4ovqQ@mail.gmail.com>

On Fri, 2015-03-06 at 12:04 +0100, Linus Walleij wrote:
> On Wed, Feb 18, 2015 at 1:18 PM, Shobhit Kumar <shobhit.kumar@intel.com> wrote:
> 
> > Export Panel BACKLIGHT_EN(offset 0x51) and PANEL_EN(offset 0x52) as two
> > additional GPIOs. Needed by display driver to enable the DSI panel on
> > BYT platform where the Panel EN/Disable and Backlight control are
> > routed thorugh CRC PMIC
> >
> > Cc: Linus Walleij <linus.walleij@linaro.org>
> > Cc: Alexandre Courbot <gnurou@gmail.com>
> > Cc: Thierry Reding <thierry.reding@gmail.com>
> > Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
> 
> This seems very unintuitive. I have a hard time believeing this:
> 
> > +#define GPIOPANELCTL           0x51
> 
> A special GPIO only designated to panel control? That is totally
> counter to the *meaning* of "general purpose input/output".
> It is not general purpose at all, it is special-purpose.
> 
> If the data sheet says a special-purpose pin is a "GPIO" when
> it isn't the map of the world (the datasheet terminology) is wrong,
> not the world, the usage is dedicated for the panel. Look
> at the usecase, not the name.
> 
> Obviously that line is only for controlling the backlight, and you
> should spin a new child device from the Inte SoC PMIC MFD hub
> and put a driver for it in drivers/video/backlight or wherever this
> goes.

There are actually two lines for Panel Power control and Backlight
enable/disable. I have already moved towards adding a new Cell device
for PWM child device and a new pwm driver for the same. That will take
care of backlight thingy. But for the Panel power control, I am at loss
for how best to program that. It is not strictly a GPIO but behaves
similarly and thought of simply extending existing gpio-crystalcove. My
next implementation(not posted yet) is having that exported by adding a
lookup table in PMIC MFD probe routine.

Regards
Shobhit

> 
> Lee: do you agree?
> 
> Yours,
> Linus Walleij

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