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

[Lars-Peter Clausen <lars@metafoo.de>]

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. Did they decide to not include the device in 
the ACPI description at all or is there a special id for INV6050+AK8975?

How does Windows decide whether there is a device or not?

> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> ---
>   drivers/iio/magnetometer/ak8975.c | 35 +++++++++++++++++++++++++++++++++++
>   1 file changed, 35 insertions(+)
>
> diff --git a/drivers/iio/magnetometer/ak8975.c b/drivers/iio/magnetometer/ak8975.c
> index 0d10a4b..c3455bd 100644
> --- a/drivers/iio/magnetometer/ak8975.c
> +++ b/drivers/iio/magnetometer/ak8975.c
> @@ -820,6 +820,36 @@ static const struct i2c_device_id ak8975_id[] = {
>
>   MODULE_DEVICE_TABLE(i2c, ak8975_id);
>
> +#if defined(CONFIG_ACPI)
> +static int ak8975_detect(struct i2c_client *temp_client,
> +			 struct i2c_board_info *info)
> +{
> +	struct i2c_adapter *adapter;
> +	int i, j;
> +	int ret;
> +
> +	/* autodetect only when we are behind a mux */
> +	adapter = i2c_parent_is_i2c_adapter(temp_client->adapter);
> +	if (!adapter)
> +		return -ENODEV;
> +
> +	for (i = 0; i < AK_MAX_TYPE; ++i) {
> +		ret = ak8975_who_i_am(temp_client, i);
> +		if (ret >= 0) {
> +			for (j = 0; j < ARRAY_SIZE(ak8975_id) - 1; ++j) {
> +				if (i == (int)ak8975_id[j].driver_data) {
> +					strlcpy(info->type, ak8975_id[j].name,
> +						I2C_NAME_SIZE);
> +					return 0;
> +				}
> +			}
> +		}
> +	}
> +
> +	return -ENODEV;
> +}
> +#endif
> +
>   static const struct of_device_id ak8975_of_match[] = {
>   	{ .compatible = "asahi-kasei,ak8975", },
>   	{ .compatible = "ak8975", },
> @@ -841,6 +871,11 @@ static struct i2c_driver ak8975_driver = {
>   	},
>   	.probe		= ak8975_probe,
>   	.id_table	= ak8975_id,
> +#if defined(CONFIG_ACPI)
> +	.class		= I2C_CLASS_HWMON,
> +	.address_list	= I2C_ADDRS(0x0C, 0x0D, 0x0E, 0x0F),
> +	.detect		= ak8975_detect,

In contrast to the commit message this is always enabled if the kernel 
contains ACPI support, not if the device is a ACPI device.

> +#endif
>   };
>   module_i2c_driver(ak8975_driver);
>
>