linux-kernel - Re: [PATCH 3/4] pinctrl: remove slew-rate parameter from tz1090

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Message-ID: <51CA0E62.2080403@wwwdotorg.org>
Date:	Tue, 25 Jun 2013 15:40:50 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	James Hogan <james.hogan@...tec.com>,
	Heiko Stübner 
	<heiko@...ech.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <rob.herring@...xeda.com>
Subject: Re: [PATCH 3/4] pinctrl: remove slew-rate parameter from tz1090

On 06/25/2013 09:39 AM, Linus Walleij wrote:
> On Tue, Jun 25, 2013 at 3:50 PM, James Hogan <james.hogan@...tec.com> wrote:
>> On 25/06/13 14:32, Linus Walleij wrote:
> 
>>> Patches adding it back in with SI measures will be welcomed!
>>
>> Okay.
>>
>> So the most descriptive documentation I can find for the slew rate in
>> the TZ1090 pin config hardware is basically:
>>
>> 0: slow (half frequency)
>> 1: fast
>>
>> Sounds like this pretty much precludes it from having a generic DT
>> binding unless it can be mapped to some physical value, so I'll add a
>> tz1090,slew-rate and use PIN_CONFIG_END+1 instead of PIN_CONFIG_SLEW_RATE.
> 
> Okay... ut the Nomadik pin controller incidentally have a
> similar definition: NMK_GPIO_LOWEMI. By slashing the
> slew rate in half the EMI is of course reduced so that was
> another name for the same thing.
> 
> Maybe this is something that should just be boolean?
> 
> slewrate-reduced-slope;

Tegra has, IIRC, 4 different slew rates. I'm not sure that a
Boolean/dual-state value would be appropriate here; it'd be limited to
supporting some arbitrary cases rather than being something generic.

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