Re: [PATCH 1/2] iio: core: add _bias channel information

[Jonathan Cameron <jic23@cam.ac.uk>]

On 09/15/11 16:04, michael.hennerich@analog.com wrote:
> From: Michael Hennerich <michael.hennerich@analog.com>
Sorry, I must be dozing, why can't this be covered by the _offset
equivalent?  Admittedly it will then be tied up with the _scale
parameter changing, but surely with a bit of care this can still be
done?

As I read it, with this we would have

X_input = (X_raw + X_offset)*X_scale + X_bias ?

Can be transformed with care to

X_input = (X_raw + X_offset + X_bias/X_scale)*X_scale 

Annoying to do, but still it would keep us in line with current abi.

We could do this, but I'm unclear on whether it is justified.

Please argue your case!

> 
> 
> Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
> ---
>  drivers/staging/iio/Documentation/sysfs-bus-iio |   16 ++++++++++++++++
>  drivers/staging/iio/iio.h                       |    2 ++
>  drivers/staging/iio/industrialio-core.c         |    1 +
>  3 files changed, 19 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/staging/iio/Documentation/sysfs-bus-iio b/drivers/staging/iio/Documentation/sysfs-bus-iio
> index 1d52c96..12e70be 100644
> --- a/drivers/staging/iio/Documentation/sysfs-bus-iio
> +++ b/drivers/staging/iio/Documentation/sysfs-bus-iio
> @@ -201,6 +201,22 @@ Description:
>  		for variation between different instances of the part, typically
>  		adjusted by using some hardware supported calibration procedure.
>  
> +What:		/sys/bus/iio/devices/iio:deviceX/in_capacitanceY_bias
> +KernelVersion:	3.1.0
> +Contact:	linux-iio@vger.kernel.org
> +Description:
> +		If known for a device, offset/bias to be added to <type>[Y]_raw
> +		post to scaling by <type>[Y]_scale in order to obtain value in
> +		the <type> units as specified in <type>[y]_raw documentation.
> +		Not present if the bias/offset is always 0 or unknown.
> +		If Y is not present, then the bias/offset applies to all in
> +		channels of <type>. May be writable if a variable offset bias
> +		can be applied on the device. Note that this is different to
> +		calibbias which is for devices (or drivers) that apply offsets
> +		to compensate for variation between different instances of the
> +		part, typically adjusted by using some hardware supported
> +		calibration procedure.
> +
>  What:		/sys/bus/iio/devices/iio:deviceX/in_voltageY_scale
>  What:		/sys/bus/iio/devices/iio:deviceX/in_voltageY_supply_scale
>  What:		/sys/bus/iio/devices/iio:deviceX/in_voltage_scale
> diff --git a/drivers/staging/iio/iio.h b/drivers/staging/iio/iio.h
> index 8ef04f8..06527ba 100644
> --- a/drivers/staging/iio/iio.h
> +++ b/drivers/staging/iio/iio.h
> @@ -83,6 +83,8 @@ enum iio_chan_info_enum {
>  	IIO_CHAN_INFO_QUADRATURE_CORRECTION_RAW_SEPARATE,
>  	IIO_CHAN_INFO_AVERAGE_RAW_SHARED,
>  	IIO_CHAN_INFO_AVERAGE_RAW_SEPARATE,
> +	IIO_CHAN_INFO_BIAS_SHARED,
> +	IIO_CHAN_INFO_BIAS_SEPARATE,
>  };
>  
>  enum iio_endian {
> diff --git a/drivers/staging/iio/industrialio-core.c b/drivers/staging/iio/industrialio-core.c
> index fd4aada..5e9a65d 100644
> --- a/drivers/staging/iio/industrialio-core.c
> +++ b/drivers/staging/iio/industrialio-core.c
> @@ -86,6 +86,7 @@ static const char * const iio_chan_info_postfix[] = {
>  	[IIO_CHAN_INFO_QUADRATURE_CORRECTION_RAW_SHARED/2]
>  	= "quadrature_correction_raw",
>  	[IIO_CHAN_INFO_AVERAGE_RAW_SHARED/2] = "mean_raw",
> +	[IIO_CHAN_INFO_BIAS_SHARED/2] = "bias",
>  };
>  
>  /**