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

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Message-ID: <51C9AFC4.1020305@imgtec.com>
Date:	Tue, 25 Jun 2013 15:57:08 +0100
From:	James Hogan <james.hogan@...tec.com>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Heiko Stübner <heiko@...ech.de>,
	Stephen Warren <swarren@...dotorg.org>,
	"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 25/06/13 14:22, Linus Walleij wrote:
> Can't we just try to come up with a patch that nails down the meaning of
> slew rate in some meaningful manner then?
> 
> So according to:
> http://en.wikipedia.org/wiki/Slew_rate
> a proper expression for slew rate would be dV/dt i.e.
> something like microvolts per microsecond (which then just
> becomes volts/second).
> 
> What we need to figure out is what range will be applicable within
> reasonable doubt for current scenarios and the next few years.
> 
> What are your datasheets specifying here, and what would be
> a proper measure?

My datasheet says:

0: slow (half frequency)
1: fast

I just got a reply back from a hardware engineer, who said that the
relationship with the actual volts/usec will depend on both the drive
strength and the load on the pad, and that a definite answer probably
requires running a simulation.

Cheers
James

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