Re: [linux-sunxi] Re: [PATCH 0/4] Add AXP209 GPIO driver

From: Hans de Goede
Date: Wed Mar 09 2016 - 10:44:20 EST


On 09-03-16 16:28, Maxime Ripard wrote:

On Wed, Mar 09, 2016 at 01:17:50PM +0100, Hans de Goede wrote:

On 09-03-16 11:50, Maxime Ripard wrote:

The axp209 PMIC used in combination to some Allwinner SoCs has a bunch
of GPIOs accessible. Some boards use these to control their backlight
or a few LEDs.

Thanks for working on this, but IMHO this cannot go upstream like this,
the gpio pins on the axp pmics need a pinctrl driver, not a gpio
driver. I.E. on the axp209 gpio0 and gpio1 can also be used to output
an additional low-noise ldo (so as a regulator), or as an adc input.

Eventually, yes, it needs both. But they don't even have to be the
same driver, since they provide two different features. The only
reason we have that construct in the pio case is because they share
the same address space, but in the AXP case, the regmap and our mfd
take care of that already.

Hmm, so your suggesting to have mfd instantiate 2 platform devices
for this, a gpio and a pinctrl device, each with their own
driver. Yes that would work, but I'm a bit worried about the 2
racing or some such since they both will end up touching
bit 0-2 of register 0x90 / 0x92, more-over since they are both
touching the exact same bits I've the feeling that this really
should be one driver.

I guess that in a proper written dts we either use pinctrl to enable
a special function, or gpio, but still.

I've been working on gsl1680 touchscreen support lately and on at least
a few a23 tablets, the low-noise ldo is used as AVCC for the touchscreen

Yeah, the AXP209 also has an ADC connected to these pins.

Now these use an axp223 pmic, but nothing is stopping someone from
doing something similar with an axp209 and I think it would be best
to support this from day one, rather then hope we can retro-fit this
later without breaking dts.

I considered that, but I don't see how it would break the DT later. If
someone wants to enable say the ADC, he will of course have to add the
pinctrl driver, and the pinctrl handles, but the old DT will only
reference the gpio driver directly, which would still be something
that would work.

I was assuming we would use one mfd-child(-platform)-device for this,
not two. I guess that with 2 devices you're right and there should
not be any problem, still as said it feels wrong-ish to have 2 drivers
poking bits 0-2 of reg 0x90 / reg 0x92.