linux-kernel - Re: [PATCH] i2c / ACPI: Pick the first address if device has multiple

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Message-ID: <20150113170007.GV1386@lahna.fi.intel.com>
Date:	Tue, 13 Jan 2015 19:00:07 +0200
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Wolfram Sang <wsa@...-dreams.de>
Cc:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c / ACPI: Pick the first address if device has multiple

On Tue, Jan 13, 2015 at 05:48:29PM +0100, Wolfram Sang wrote:
> On Tue, Jan 13, 2015 at 08:44:37AM -0800, Srinivas Pandruvada wrote:
> > On Tue, 2015-01-13 at 16:50 +0100, Wolfram Sang wrote: 
> > > On Mon, Dec 29, 2014 at 03:48:48PM +0200, Mika Westerberg wrote:
> > > > ACPI specification allows I2C devices with multiple addresses. The current
> > > > implementation goes over all addresses and assigns the last one to the
> > > > device. This is typically not the primary address of the device.
> > > > 
> > > > Instead of doing that we assign the first address to the device and then
> > > > let the driver handle rest of the addresses as it wishes.
> > > > 
> > > > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > > > Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> > > 
> > > Yes, seems better than what we do know. But maybe taking the lowest
> > > address is a bit better heuristic than taking the first address?
> > > Not sure, though...
> > The problem in taking lowest is that in many cases in current devices,
> > the lowest address may end being 0x0C, which is reserved address for
> > SMBUS (ARA). This will require different handling. Unfortunately ACPI
> > doesn't have a way to distinguish whether SMBUS support is desired or
> > not. 
> > The other option is to skip all reserved addresses for SMBUS also and
> > then create on the lowest.
> 
> Well, this makes me think that Mika's approach is probably the sanest
> one...

Also I think it is more consistent that way.
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