linux-kernel - Re: Smartcard/SIM card subsystem, LDO regulator and signal modelling

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Message-ID: <20110518162558.GA16414@opensource.wolfsonmicro.com>
Date:	Wed, 18 May 2011 09:25:58 -0700
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	linux-kernel@...r.kernel.org,
	Bibek BASU <bibek.basu@...ricsson.com>,
	Sascha Hauer <kernel@...gutronix.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Juergen Beisert <jbe@...gutronix.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: Smartcard/SIM card subsystem, LDO regulator and signal modelling

On Wed, May 18, 2011 at 12:36:17PM +0200, Linus Walleij wrote:

> It's basically an LDO for powering a SIM card (which in turn is basically
> a smartcard), but apart from plain regulation also expose some other
> electrical properties of the interface to software:

> - Select pull-up resistance on some I/O lines
> - Select weak pull-down on some data lines
> - Select load capacitance limits on the data lines
> - Select whether to run in low impedance or transmission gate mode

> I think these will be mostly similar so what other SIM card controllers
> will need to have. All the stuff needs to have userspace interfaces
> since the stuff is usually controlled on behalf of another CPU
> running the modem (and also performing the actual traffic on
> the SIM data lines).

The above also sounds rather like the standard sort of stuff you get
with pin muxes - the pulls are certainly very common for random GPIO
or I2C use, for example.  No real idea on the SIM interface itself.
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