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

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Date:	Tue, 13 Jan 2015 17:48:29 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:	Mika Westerberg <mika.westerberg@...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 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...


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