Re: [PATCH 3/3] iio: ak8975: Added autodetect feature for ACPI

[Lars-Peter Clausen <lars-Qo5EllUWu/uELgA04lAiVw@public.gmane.org>]

On 12/18/2014 06:30 PM, Srinivas Pandruvada wrote:
> On Thu, 2014-12-18 at 18:05 +0100, Lars-Peter Clausen wrote:
>> On 12/18/2014 05:52 PM, Srinivas Pandruvada wrote:
>>> On Thu, 2014-12-18 at 17:28 +0100, Lars-Peter Clausen wrote:
>>>> Added I2C to Cc.
>>>>
>>>> On 12/15/2014 10:19 PM, Srinivas Pandruvada wrote:
>>>>> Using i2c auto detect feature and auto device creation feature,
>>>>> enumerate ak8975 device, by checking their presence.
>>>>> This is needed because when this device sits behind an i2c mux, there
>>>>> is no way to define i2c mux in ACPI. This will enable ak8975 on
>>>>> windows based tablets/laptops running Linux when connected via a mux.
>>>>> Since DT model already can define an i2c mux and devices connected to
>>>>> it, this feature is only enabled for ACPI.
>>>>>
>>>>
>>>> This is quite a bit of a hack.
>>> Why?
>>> Auto detect is standard feature of i2c devices. This is using standard
>>> auto detect feature provided by the framework.
>>
>> Auto detect is ugly, slow and unreliable, it's kind of like the last straw
>> if nothing else works.
> That is true here. You can't enumerate this device by ACPI. As discussed
> before we created i2c mux in inv6050 so that we can use AK8975 in bypass
> mode. I added some API to create i2c device on this mux, which Wolfram
> didn't like. He wanted to enumerate using existing mechanisms.

If there is only a single ACPI ID that says this is a INV6050 with a AK8975 
attached then the way to handle this is to have a driver that binds to that id 
and creates both devices.

- Lars