Date:   Mon, 12 Sep 2016 09:33:03 -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 1/2] iio: Implement counter channel type and info
 constants

On Sat, Sep 10, 2016 at 05:11:56PM +0100, Jonathan Cameron wrote:
>On 07/09/16 18:55, 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.
>This is interesting.  There is clearly an overlap in functionality with
>the resolver drivers (which are all still hiding in staging
><gives Lars a gentle reminder>)
>but the very nature of them is that we know the correspondence between
>their output and a physical angle.
>
>Here we have no way of knowing that.  The very nature of such systems
>is they aren't always hardwired to a particular encoder so even in
>embedded systems that translation probably isn't something we can
>directly push into the device tree.
>
>I wonder if ultimately we might want a consumer driver taking the
>'counts' of a raw quadrature encoder interface and converting that
>(with additional information provided either from DT or configfs)
>to an angle etc. 
>
>Job for another day ;)

Ultimately, some sort consumer driver would be quite useful I would
imagine. Afterall, quadrature encoder counters are rarely used for the
sole sake of counting rising edges. Rather, maintaining counts is simply
one step of the ultimate process of encoding/decoding some real world
data (position, distance, angle, etc.), be it for a conveyor belt, 3-D
printer, CNC mill, or any other sort of industrial automation or robotic
system.

Providing an interface to access the ultimate real world data directly
would be very apt. Though of course, there would be a variety of common
real world values for which would need to be accounted (e.g. distance
versus angle).

>
>I did wonder if we could 'abuse' the steps channel type to
>avoid adding a new one (particularly as I've been eyeing up
>some ST powerstep01 all in one stepper driver chips at work
>and thinking they really should have a kernel driver ;)
>
>Probably not though...
>
>I think we need to think long and hard about the ABI for this
>and try and make it a bit clearer / more generic in some ways
>from the start.

With this I very much agree. While encoders are ubiquitous in the
industrial sector, their uses are quite diverse. The ABI should be clear
and generic enough to interface with the majority of these types of
devices and expose their data without restricting their use cases. Be
quick to point out any possible problem paths early on lest we
unintentionally restrict this ABI to only a subset of devices.

>> 
>>   IIO_COUNT: Current count (main data provided by the counter device)
>> 
>>   IIO_CHAN_INFO_FLAGS: Counter flag states (e.g. underflows, overflows,
>>                        errors, etc.)
>Probably not suitable for an IIO_CHAN_INFO element.  There are lots
>of things that hide in here that should be broken out separately
>(and probably via ext_info elements at that).
>>   IIO_CHAN_INFO_DIRECTION: Set high when counting up and reset low when
>>                            counting down
>Should indicate this in it's name.
>IIO_CHAN_INFO_INCREASING perhaps?
>>   IIO_CHAN_INFO_INDEX: Set high when index input is at active level
>Hmm. might be something we want to do in a buffer at somepoint so
>might want to be a channel type in it's own right..
>>   IIO_CHAN_INFO_MODE: Count value encoding, counter range setting,
>>                       quadrature phase mode, etc.
>Another one where we are throwing lots of things into one hole.
>Have separate ext_info elements instead breaking these out.
>
>>   IIO_CHAN_INFO_PRESET: Counter preset value
>Fair enough on this one.
>
>>   IIO_CHAN_INFO_PRESET_EN: Set high to preset counter on signal (e.g.
>>                            index input at active level)
>Hmm. This needs more care as we probably want one ext_info element
>that has values 'disabled', 'index high' etc.

I'll submit a second version of this patch with the changes you
suggested. Using ext_info elements should break out the flags, mode, and
other indicated data more suitably.

William Breathitt Gray

>
>> 
>> Signed-off-by: William Breathitt Gray <vilhelm.gray@...il.com>
>> ---
>>  drivers/iio/industrialio-core.c | 7 +++++++
>>  include/linux/iio/iio.h         | 6 ++++++
>>  include/uapi/linux/iio/types.h  | 1 +
>>  3 files changed, 14 insertions(+)
>> 
>> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
>> index 0528a0c..bfdb09d 100644
>> --- a/drivers/iio/industrialio-core.c
>> +++ b/drivers/iio/industrialio-core.c
>> @@ -81,6 +81,7 @@ static const char * const iio_chan_type_name_spec[] = {
>>  	[IIO_PH] = "ph",
>>  	[IIO_UVINDEX] = "uvindex",
>>  	[IIO_ELECTRICALCONDUCTIVITY] = "electricalconductivity",
>> +	[IIO_COUNT] = "count",
>>  };
>>  
>>  static const char * const iio_modifier_names[] = {
>> @@ -151,6 +152,12 @@ 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_FLAGS] = "flags",
>> +	[IIO_CHAN_INFO_DIRECTION] = "direction",
>> +	[IIO_CHAN_INFO_INDEX] = "index",
>> +	[IIO_CHAN_INFO_MODE] = "mode",
>> +	[IIO_CHAN_INFO_PRESET] = "preset",
>> +	[IIO_CHAN_INFO_PRESET_EN] = "preset_enable",
>>  };
>>  
>>  /**
>> diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
>> index b4a0679..13543fd 100644
>> --- a/include/linux/iio/iio.h
>> +++ b/include/linux/iio/iio.h
>> @@ -46,6 +46,12 @@ enum iio_chan_info_enum {
>>  	IIO_CHAN_INFO_DEBOUNCE_TIME,
>>  	IIO_CHAN_INFO_CALIBEMISSIVITY,
>>  	IIO_CHAN_INFO_OVERSAMPLING_RATIO,
>> +	IIO_CHAN_INFO_FLAGS,
>> +	IIO_CHAN_INFO_DIRECTION,
>> +	IIO_CHAN_INFO_INDEX,
>> +	IIO_CHAN_INFO_MODE,
>> +	IIO_CHAN_INFO_PRESET,
>> +	IIO_CHAN_INFO_PRESET_EN,
>>  };
>>  
>>  enum iio_shared_by {
>> diff --git a/include/uapi/linux/iio/types.h b/include/uapi/linux/iio/types.h
>> index 22e5e58..e227039 100644
>> --- a/include/uapi/linux/iio/types.h
>> +++ b/include/uapi/linux/iio/types.h
>> @@ -40,6 +40,7 @@ enum iio_chan_type {
>>  	IIO_PH,
>>  	IIO_UVINDEX,
>>  	IIO_ELECTRICALCONDUCTIVITY,
>> +	IIO_COUNT,
>>  };
>>  
>>  enum iio_modifier {
>> 
>

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