linux-kernel - Re: [PATCH v4 1/2] iio: Implement counter channel type and info constants

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Date:   Tue, 27 Sep 2016 14:30:42 -0400
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     knaack.h@....de, lars@...afoo.de, pmeerw@...erw.net,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] iio: Implement counter channel type and info
 constants

On Sat, Sep 24, 2016 at 06:03:21PM +0100, Jonathan Cameron wrote:
>On 21/09/16 21:15, William Breathitt Gray wrote:
>> Quadrature encoders, such as rotary encoders and linear encoders, are
>> devices which are capable of encoding the relative position and
>> direction of motion of a shaft. This patch introduces several IIO
>> constants for supporting quadrature encoder counter devices.
>> 
>>   IIO_COUNT: Current count (main data provided by the counter device)
>>   IIO_INDEX: Counter device index value
>>   IIO_CHAN_INFO_PRESET: Counter preset value
>> 
>> Signed-off-by: William Breathitt Gray <vilhelm.gray@...il.com>
>> ---
>>  Documentation/ABI/testing/sysfs-bus-iio | 28 ++++++++++++++++++++++++++++
>>  drivers/iio/industrialio-core.c         |  3 +++
>>  include/linux/iio/iio.h                 |  1 +
>>  include/uapi/linux/iio/types.h          |  2 ++
>>  4 files changed, 34 insertions(+)
>> 
>> diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
>> index fee35c0..be66a41 100644
>> --- a/Documentation/ABI/testing/sysfs-bus-iio
>> +++ b/Documentation/ABI/testing/sysfs-bus-iio
>> @@ -1579,3 +1579,31 @@ Contact:	linux-iio@...r.kernel.org
>>  Description:
>>  		Raw (unscaled no offset etc.) electric conductivity reading that
>>  		can be processed to siemens per meter.
>> +
>> +What:		/sys/bus/iio/devices/iio:deviceX/in_countY_raw
>> +KernelVersion:	4.9
>> +Contact:	linux-iio@...r.kernel.org
>> +Description:
>> +		Raw counter device counts from channel Y. For quadrature
>> +		counters, division by an available [Y]_scale results in the
>> +		counts of a single quadrature signal phase from channel Y.
>Division?  Needs to be multiplication to be consistent with the other
>interfaces.  

That makes sense. What I'll do is refactor scale to accept the values 1,
0.5, and 0.25 to select the respective x1, x2, and x4 quadrature modes.

The counter device will count full-phase edges on quadrature x1 mode,
half-phase edges on quadrature x2 mode (twice as many counts as x1), and
quarter-phase edges on quadrature x4 mode (twice as many counts as x2).
One of the benefits of the x2 and x4 quadrature modes is increased
position fidelity, so exposing scale as a fraction will allow it to be
multipled to raw counts without sacrificing the precision benefit of the
x2 and x4 quadrature modes.

William Breathitt Gray

>> +
>> +What:		/sys/bus/iio/devices/iio:deviceX/in_countY_scale
>> +KernelVersion:	4.9
>> +Contact:	linux-iio@...r.kernel.org
>> +Description:
>> +		If a scale value is available for channel Y, it is provided by
>> +		this attribute.
>Can just add the What line to the big block of _scale attributes already
>listed.  Generic text should cover it fine.
>> +
>> +What:		/sys/bus/iio/devices/iio:deviceX/in_countY_preset
>> +KernelVersion:	4.9
>> +Contact:	linux-iio@...r.kernel.org
>> +Description:
>> +		If the counter device supports preset registers, the preset
>> +		count for channel Y is provided by this attribute.
>> +
>> +What:		/sys/bus/iio/devices/iio:deviceX/in_indexY_raw
>> +KernelVersion:	4.9
>> +Contact:	linux-iio@...r.kernel.org
>> +Description:
>> +		Raw counter device index value from channel Y.
>Needs more description.  Don't assume people have any idea what an 'index'
>value is on a counter.
>> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
>> index fc340ed..ed175a2 100644
>> --- a/drivers/iio/industrialio-core.c
>> +++ b/drivers/iio/industrialio-core.c
>> @@ -81,6 +81,8 @@ static const char * const iio_chan_type_name_spec[] = {
>>  	[IIO_PH] = "ph",
>>  	[IIO_UVINDEX] = "uvindex",
>>  	[IIO_ELECTRICALCONDUCTIVITY] = "electricalconductivity",
>> +	[IIO_COUNT] = "count",
>> +	[IIO_INDEX] = "index",
>>  };
>>  
>>  static const char * const iio_modifier_names[] = {
>> @@ -151,6 +153,7 @@ static const char * const iio_chan_info_postfix[] = {
>>  	[IIO_CHAN_INFO_DEBOUNCE_TIME] = "debounce_time",
>>  	[IIO_CHAN_INFO_CALIBEMISSIVITY] = "calibemissivity",
>>  	[IIO_CHAN_INFO_OVERSAMPLING_RATIO] = "oversampling_ratio",
>> +	[IIO_CHAN_INFO_PRESET] = "preset",
>>  };
>>  
>>  /**
>> diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
>> index b4a0679..7dc86d1 100644
>> --- a/include/linux/iio/iio.h
>> +++ b/include/linux/iio/iio.h
>> @@ -46,6 +46,7 @@ enum iio_chan_info_enum {
>>  	IIO_CHAN_INFO_DEBOUNCE_TIME,
>>  	IIO_CHAN_INFO_CALIBEMISSIVITY,
>>  	IIO_CHAN_INFO_OVERSAMPLING_RATIO,
>> +	IIO_CHAN_INFO_PRESET,
>>  };
>>  
>>  enum iio_shared_by {
>> diff --git a/include/uapi/linux/iio/types.h b/include/uapi/linux/iio/types.h
>> index 22e5e58..e54d14a 100644
>> --- a/include/uapi/linux/iio/types.h
>> +++ b/include/uapi/linux/iio/types.h
>> @@ -40,6 +40,8 @@ enum iio_chan_type {
>>  	IIO_PH,
>>  	IIO_UVINDEX,
>>  	IIO_ELECTRICALCONDUCTIVITY,
>> +	IIO_COUNT,
>> +	IIO_INDEX,
>>  };
>>  
>>  enum iio_modifier {
>> 
>