linux-kernel - RE: [PATCH] i2c-gpio.c: correct logic of pdata->scl_is_open

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Date:	Wed, 2 Nov 2011 06:56:50 +0100
From:	"Voss, Nikolaus" <N.Voss@...nmann.de>
To:	"'H Hartley Sweeten'" <hartleys@...ionengravers.com>,
	'Håvard Skinnemoen' <hskinnemoen@...il.com>
CC:	"'Linux Kernel'" <linux-kernel@...r.kernel.org>,
	"'linux-arm-kernel@...ts.infradead.org'" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH] i2c-gpio.c: correct logic of pdata->scl_is_open_drain

> If the "is_open_drain" flags are not set, the I2C bus works correctly
> regardless of the existence of the pull-ups.

No, I2C can only work with anything pulling up SDA weakly, usually an
external pullup. This is independent of the "is_open_drain" property
which only describes how the driver internally accomplishes the high
impedance state.

SCL can be driven push-pull ("scl_is_output_only") but will not be
I2C-compliant any more (no clock stretching), and only clients not relying
on that feature will work.

Niko

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