linux-kernel - Re: [rtc-linux] [PATCH V2 3/5] gpio: add support for AMS AS3722 gpio driver

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Date:	Mon, 23 Sep 2013 14:25:15 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	"rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>,
	Lee Jones <lee.jones@...aro.org>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Mark Brown <broonie@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Rob Landley <rob@...dley.net>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	Grant Likely <grant.likely@...aro.org>,
	Florian Lobmaier <florian.lobmaier@....com>
Subject: Re: [rtc-linux] [PATCH V2 3/5] gpio: add support for AMS AS3722 gpio
 driver

On Monday 23 September 2013 01:36 PM, Linus Walleij wrote:
> On Fri, Sep 20, 2013 at 2:30 PM, Laxman Dewangan <ldewangan@...dia.com> wrote:
>
>> +Required subnode properties:
>> +---------------------------
>> +reg: The GPIO number on which the properties need to be applied.
>> +
>> +Optional subnode properties:
>> +---------------------------
>> +bias-pull-up: The Pull-up for the pin to be enable.
>> +bias-pull-down: Pull down of the pins to be enable.
>> +bias-high-impedance: High impedance of the pin to be enable.
>> +open-drain: Pin is open drain type.
>> +function: IO functionality of the pins. The valid options are:
>> +       gpio, intrrupt-output, vsup-vbat-low-undeb, interrupt-input,
>> +       pwm-input, voltage-stby, oc-powergood-sd0, powergood-output,
>> +       clk32k-output, watchdog-input, soft-reset-input, pwm-output,
>> +       vsup-vbat-low-deb, oc-powergood-sd6
>> +    Missing the function property will set the pin in GPIO mode.
> This is pin control. Do not try to shoehorn pin control drivers into
> the GPIO subsystem. Take a good day off, read through
> Documentation/pinctrl.txt and come back with a thoroughly rewritten
> driver in drivers/pinctrl/pinctrl-as3722.c.
>
> We already have generic device tree bindings for all of the above
> properties, and a library for generic pin config in the pin control
> subsystem to handle them. Look at recent drivers for
> inspiration.
>

Yes, the appropriate location is pin control for pull up/down etc 
configuration but with this device, the actual issue is with the way it 
is require to configure the pull up/down and input/output of the pin. 
There is no separate bits for pull up/down and direction and it is  
clubbed together. The register's bits are defined as:

Selects the GPIO mode (I, I/O, Tri, Pulls) (BIT 2:0)
   0 : Input
   1 : Output (push and pull) VSUP_GPIO
   2 : Output/Input (open drain, only NMOS is active)
   3 : ADC input (Tristate)
   4 : Input with pull-up to VDD_GPIO_lv
   5 : Input with pull-down
   6 : Output/Input open drain (nmos) with pull-up to VDD_GPIO_lv,
   7 : Output (push and pull) VDD_GPIO_lv

So I can not actually configure the pull up/down, open drain and 
direction independently until every thing is known.
Direction come from gpio driver but pull up/down and open drain 
configuration come from the pin control.
And this is only the reason to make all configuration in single driver.







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