linux-kernel - Re: [PATCH 07/10] pinctrl: add pinctrl driver for Rockchip SoCs

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Date:	Wed, 5 Jun 2013 09:01:44 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Heiko Stübner <heiko@...ech.de>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Turquette <mturquette@...aro.org>,
	Seungwon Jeon <tgih.jun@...sung.com>,
	Jaehoon Chung <jh80.chung@...sung.com>,
	Chris Ball <cjb@...top.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>
Subject: Re: [PATCH 07/10] pinctrl: add pinctrl driver for Rockchip SoCs

On Tue, Jun 4, 2013 at 2:05 PM, Heiko Stübner <heiko@...ech.de> wrote:

>> > +PULL_AUTO      (1 << 0): indicate this pin needs a pull setting for SoCs
>> > +                         that determine the pull up or down themselfs
>>
>> Hm, never saw that before...
>
> Citing the original gpio driver:
>
>         /*
>          * Values written to this register independently
>          * control Pullup/Pulldown or not for the
>          * corresponding data bit in GPIO.
>          * 0: pull up/down enable, PAD type will decide
>          * to be up or down, not related with this value
>          * 1: pull up/down disable
>          */
>
> So if it's a pull up or down is decided based on the mux of the pin. Calling
> everything a "pull down" (or up) when it isn't seemed somehow wrong to me.
>
> The rk3188 on the other hand supports both pull up and down separately.
>
> Or should this be selected as PULL_UP | PULL_DOWN in the config?

The generic config is pretty much either/or so it'd be a new
config for that approach.

Basically it seems they have embedded knowledge into the
silicon: there is no specific rule as to whether a pad should be
pulled up or down depending on "pad type" as is stated, rather
it's so that if you know a pad will be used for I2C SCL then
you know it needs pull-up. Probably something like a "1" on
some constant switch in VHDL/Verilog is hard-coded into
the silicon turning on pull-up if I2C is selected and the
autopull is set for example.

>> +config PINCTRL_ROCKCHIP
>> +       bool
>> +       select PINMUX
>> +       select PINCONF
>> +       select GENERIC_IRQ_CHIP
>>
>> Why is this super-simple pin config thing not using
>> GENERIC_PINCONF?
>>
>> I *know* it is simpler to implement your own thing, but think of the
>> poor maintainers that have to wade through 50 identical implementations.
>> Do this, it pays off.
>
> generic pinconf sounds interesting ... will give it a try.
>
> The only problem is the pull stuff mentioned above that is either pull up or
> down without the driver having knowledge about it. And generic_pinconf only
> knows about them separately right now.

Create a separate patch adding PIN_CONFIG_BIAS_PULL_AUTO
to include/linux/pinctrl/pinconf-generic.h, don't forget the
kerneldoc, and patching drivers/pinctrl/pinconf-generic.c.

I'll apply it right away.

>> Nothing else you want to say about the pins here?
>> (No big deal for sure, but....)
>
> when using pinconfig_generic, its dump_pin function should be more talkative
> right?

Yes, one of the things you get for free... soon also the pin config
DT parser will be for free I hope.

Yours,
Linus Walleij
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