linux-kernel - Re: [PATCH 2/2] iio: accel: bmc150: Check for a second ACPI device for BOSC0200

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Message-ID: <20171205112738.00006ffd@huawei.com>
Date:   Tue, 5 Dec 2017 11:27:38 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
CC:     Jonathan Cameron <jic23@...nel.org>,
        Jeremy Cline <jeremy@...ine.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        "Peter Meerwald-Stadler" <pmeerw@...erw.net>,
        Hans de Goede <hdegoede@...hat.com>,
        Lars Kellogg-Stedman <lars@...bit.com>,
        Steven Presser <steve@...ssers.name>,
        <linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Wolfram Sang <wsa@...-dreams.de>
Subject: Re: [PATCH 2/2] iio: accel: bmc150: Check for a second ACPI device
 for BOSC0200

On Mon, 4 Dec 2017 11:58:19 +0200
Mika Westerberg <mika.westerberg@...ux.intel.com> wrote:

> On Sat, Dec 02, 2017 at 12:19:27PM +0000, Jonathan Cameron wrote:
> > On Wed, 29 Nov 2017 22:31:12 +0000
> > Jeremy Cline <jeremy@...ine.org> wrote:
> >   
> > > Some BOSC0200 acpi_device-s describe two accelerometers in a single ACPI
> > > device. Check for a companion device and handle a second i2c_client
> > > if it is present.  
> > 
> > + Mika and Wolfram - please cc them on anything odd and i2c / ACPI related.
> > (I like to share the pain)
> > 
> > My usual question, just out of curiosity as we have to cope with this
> > fun anyway.  Are you actually allowed to do this under the ACPI spec
> > or not?  I would assume an acpi device is supposed to be just that A
> > device...  I fall asleep every time I try to read that spec ;)  
> 
> Yes, it is allowed. Typically you have an ACPI device and it can have
> multiple I2cSerialBus() connections.
> 
> Linux ACPI/I2C core then picks the first one and creates i2c_client from
> that but the additional connections need to be created by the driver in
> question.

Why does it not make sense to just create them all from the ACPI/I2C core?

> 
> BTW, there is a function i2c_new_secondary_device() that is supposed to
> be used for this but it does not have ACPI support yet (maybe it is good
> time to add it now, with this patch series?)
> --
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