linux-kernel - Re: [PATCH 2/2] iio: add Bosch BMA180 acceleration sensor driver

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Date:	Sun, 04 Aug 2013 15:45:48 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Oleksandr Kravchenko <x0199363@...com>
CC:	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, grant.likely@...aro.org,
	rob.herring@...xeda.com, rob@...dley.net, jic23@....ac.uk,
	pmeerw@...erw.net, holler@...oftware.de,
	srinivas.pandruvada@...el.com, devicetree-discuss@...ts.ozlabs.org,
	Oleksandr Kravchenko <o.v.kravchenko@...ballogic.com>
Subject: Re: [PATCH 2/2] iio: add Bosch BMA180 acceleration sensor driver

On 07/29/2013 04:58 PM, Oleksandr Kravchenko wrote:
> From: Oleksandr Kravchenko <o.v.kravchenko@...ballogic.com>
> 
> This patch adds IIO driver for Bosch BMA180 triaxial
> acceleration sensor.
> http://omapworld.com/BMA180_111_1002839.pdf
> 
> Signed-off-by: Oleksandr Kravchenko <o.v.kravchenko@...ballogic.com>
> ---
>  .../devicetree/bindings/iio/accel/bma180.txt       |   53 +++
>  drivers/iio/accel/Kconfig                          |   10 +
>  drivers/iio/accel/Makefile                         |    2 +
>  drivers/iio/accel/bma180.c                         |  462 ++++++++++++++++++++
>  4 files changed, 527 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/accel/bma180.txt
>  create mode 100644 drivers/iio/accel/bma180.c
> 
> diff --git a/Documentation/devicetree/bindings/iio/accel/bma180.txt b/Documentation/devicetree/bindings/iio/accel/bma180.txt
> new file mode 100644
> index 0000000..7c13c84
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/accel/bma180.txt
> @@ -0,0 +1,53 @@
> +* Bosch BMA180 triaxial acceleration sensor
> +
> +http://omapworld.com/BMA180_111_1002839.pdf
> +
> +Required properties:
> +
> +  - compatible : should be "bosch,bma180"
> +  - reg : the I2C address of the sensor
> +
> +Optional properties:
> +
> +  - interrupt-parent : should be the phandle for the interrupt controller
> +
> +  - interrupts : interrupt mapping for GPIO IRQ, it shuld by configured with
> +		flags IRQ_TYPE_LEVEL_HIGH | IRQ_TYPE_EDGE_RISING
> +
> +  - range : select the full scale acceleration range
> +		0 : -1g..+1g
> +		1 : -1.5g..+1.5g
> +		2 : -2g..+2g
> +		3 : -3g..+3g
> +		4 : -4g..+4g
> +		5 : -8g..+8g
> +		6 : -16g..+16g
> +
> +  - bw : select bandwidth bandwidth
> +		0 : 10Hz
> +		1 : 20Hz
> +		2 : 40Hz
> +		3 : 75Hz
> +		4 : 150Hz
> +		5 : 300Hz
> +		Don't use bandwidth frequency more than 300Hz couse it
> +		influences the frequency of generating new data interrupts
> +		and i2c reading phase can be longer than pheriod of interrupt
> +		generation.
> +
> +  - mode_config : 0 - select low noise mode, 1 - select low power mode
> +
> +  - fuzz : specifies fuzz value that is used to filter noise from the event stream
> +

All the four properties above are vendor specific, so they need a vendor
prefix. Also no underscores in property names and no abbreviations. Also I
wonder if some of them should rather be runtime configurable, like range and
bandwidth,

> +Example:
> +
> +bma180@40 {
> +	compatible = "bosch,bma180";
> +	reg = <0x40>;
> +	interrupt-parent = <&gpio6>;
> +	interrupts = <18 (IRQ_TYPE_LEVEL_HIGH | IRQ_TYPE_EDGE_RISING)>;
> +	range = <2>;
> +	bw = <0>;
> +	mode_config = <1>;
> +	fuzz = <555>;
> +};
[...]
> +static int bma180_read_raw(struct iio_dev *indio_dev,
> +		struct iio_chan_spec const *chan, int *val, int *val2,
> +		long mask)
> +{
> +	struct bma180_data *data = iio_priv(indio_dev);
> +	long tmp = ((s16)data->acc_reg[chan->channel] >> 2)
> +		* bma180_range_table[data->range].ratio;

> +
> +	if (data->acc_reg[chan->channel] < 0)
> +		return data->acc_reg[chan->channel];
> +
> +	*val = tmp / 1000000;
> +	*val2 = (tmp % 1000000);
> +

This doesn't look as if the device needs a special conversion formula. Just
expose the raw value and ratio as the scale.

> +	return IIO_VAL_INT_PLUS_MICRO;
> +}
[...]
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