linux-kernel - Re: [PATCH 2/3] spi / ACPI: add ACPI enumeration support

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Message-ID: <20121106081144.GB3283@opensource.wolfsonmicro.com>
Date:	Tue, 6 Nov 2012 09:11:45 +0100
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-kernel@...r.kernel.org, lenb@...nel.org,
	rafael.j.wysocki@...el.com, grant.likely@...retlab.ca,
	linus.walleij@...aro.org, khali@...ux-fr.org, ben-linux@...ff.org,
	w.sang@...gutronix.de, mathias.nyman@...ux.intel.com,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH 2/3] spi / ACPI: add ACPI enumeration support

On Mon, Nov 05, 2012 at 02:02:19PM +0200, Mika Westerberg wrote:
> On Mon, Nov 05, 2012 at 11:56:39AM +0100, Mark Brown wrote:

> > I've got practical systems where there are multiple buses physically
> > connected, though in practice almost always only one is actually used at
> > runtime when it's I2C and SPI there are some systems (usually with other
> > buses) where you might want to use more than one bus.  Not sure those
> > buses will fit in here though.

> Yeah, I just went through DSDT table of one of our machines and found a
> device that actually has two I2CSerialBus connectors (and those are to the
> same controller). What I'm not sure is that is it used to select between
> two different addresses or doest the device really have two physical I2C
> connections.

That one is likely to be one device that responds on two addresses as
others have mentioned.  You do also get devices which have multiple
physical interfaces for various reasons, such as having a dedicated bus
for some functions that need to respond quickly.

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