linux-kernel - Re: [PATCH v2 1/4] pinctrl: add samsung pinctrl and gpiolib driver

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Message-ID: <5033FFE0.5070209@wwwdotorg.org>
Date:	Tue, 21 Aug 2012 15:38:40 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Thomas Abraham <thomas.abraham@...aro.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, grant.likely@...retlab.ca,
	rob.herring@...xeda.com, kgene.kim@...sung.com,
	Dong Aisheng <dong.aisheng@...aro.org>
Subject: Re: [PATCH v2 1/4] pinctrl: add samsung pinctrl and gpiolib driver

On 08/21/2012 05:25 AM, Linus Walleij wrote:
> On Wed, Aug 15, 2012 at 9:57 PM, Thomas Abraham
> <thomas.abraham@...aro.org> wrote:
> 
>> Add a new device tree enabled pinctrl and gpiolib driver for Samsung
>> SoC's.
...
>> +  The child node can also optionally specify one or more of the pin
>> +  configuration that should be applied on all the pins listed in the
>> +  "samsung,pins" property of the child node. The following pin configuration
>> +  properties are supported.
>> +
>> +  - samsung,pin-pud: Pull up/down configuration.
>> +  - samsung,pin-drv: Drive strength configuration.
>> +  - samsung,pin-pud-pdn: Pull up/down configuration in power down mode.
>> +  - samsung,pin-drv-pdn: Drive strength configuration in power down mode.
> 
> This looks a bit scary, as it seems to be orthogonal to the pin config
> interface. I.e. this will be programmed "behind the back" of the
> pin config system. However as long as the pin config implementation
> reads back these things from the registers it will work, too.
> 
> In the U300 and Ux500 I explicitly use pin config hogs to set up
> the pin configuration, and when we enter a state such as
> "default" the mux setting and config settings are set from the
> framework separately.

I know that some HW has a separate set of registers (or fields) for the
"awake" and "sleep" configuration, and the HW switches between the two
automatically when sleeping. I have no idea if the Samsung SoCs do this,
but I think if this were the case, it'd be quite legitimate to define
both these HW states as separate sets of properties within a single
pinctrl SW state. So, that might be the explanation here?

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