Date:   Sat, 12 Oct 2019 10:51:19 -0400
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
        patrick.havelange@...ensium.com, fabrice.gasnier@...com,
        mcoquelin.stm32@...il.com, alexandre.torgue@...com,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, benjamin.gaignard@...aro.org,
        david@...hnology.com
Subject: Re: [PATCH v5 0/3] Simplify count_read/count_write/signal_read

On Sat, Oct 12, 2019 at 03:00:12PM +0100, Jonathan Cameron wrote:
> Hi William
> 
> What's the status on these? If you are happy that reviews and
> testing is complete enough, do you want me to take them after
> I pick up the eqep driver (hopefully shortly dependent on
> the pull request Greg has from me being fine).
> 
> Thanks,
> 
> Jonathan

Yes, this is ready for you to take. So after the eqep driver is picked
up you can apply this patchset.

Thanks,

William Breathitt Gray

> 
> On Sun,  6 Oct 2019 16:03:08 -0400
> William Breathitt Gray <vilhelm.gray@...il.com> wrote:
> 
> > Changes in v5:
> >  - Add changes and additions to generic-counter.rst to clarify theory
> >    and use of the Generic Counter interface
> >  - Fix typo in counter.h action_get description comment
> > 
> > The changes in this patchset will not affect the userspace interface.
> > Rather, these changes are intended to simplify the kernelspace Counter
> > callbacks for counter device driver authors.
> > 
> > The following main changes are proposed:
> > 
> > * Retire the opaque counter_count_read_value/counter_count_write_value
> >   structures and simply represent count data as an unsigned integer.
> > 
> > * Retire the opaque counter_signal_read_value structure and represent
> >   Signal data as a counter_signal_value enum.
> > 
> > These changes should reduce some complexity and code in the use and
> > implementation of the count_read, count_write, and signal_read
> > callbacks.
> > 
> > The opaque structures for Count data and Signal data were introduced
> > originally in anticipation of supporting various representations of
> > counter data (e.g. arbitrary-precision tallies, floating-point spherical
> > coordinate positions, etc). However, with the counter device drivers
> > that have appeared, it's become apparent that utilizing opaque
> > structures in kernelspace is not the best approach to take.
> > 
> > I believe it is best to let userspace applications decide how to
> > interpret the count data they receive. There are a couple of reasons why
> > it would be good to do so:
> > 
> > * Users use their devices in unexpected ways.
> > 
> >   For example, a quadrature encoder counter device is typically used to
> >   keep track of the position of a motor, but a user could set the device
> >   in a pulse-direction mode and instead use it to count sporadic rising
> >   edges from an arbitrary signal line unrelated to positioning. Users
> >   should have the freedom to decide what their data represents.
> > 
> > * Most counter devices represent data as unsigned integers anyway.
> > 
> >   For example, whether the device is a tally counter or position
> >   counter, the count data is represented to the user as an unsigned
> >   integer value. So specifying that one device is representing tallies
> >   while the other specifies positions does not provide much utility from
> >   an interface perspective.
> > 
> > For these reasons, the count_read and count_write callbacks have been
> > redefined to pass count data directly as unsigned long instead of passed
> > via opaque structures:
> > 
> >         count_read(struct counter_device *counter,
> >                    struct counter_count *count, unsigned long *val);
> >         count_write(struct counter_device *counter,
> >                     struct counter_count *count, unsigned long val);
> > 
> > Similarly, the signal_read is redefined to pass Signal data directly as
> > a counter_signal_value enum instead of via an opaque structure:
> > 
> >         signal_read(struct counter_device *counter,
> >                     struct counter_signal *signal,
> >                     enum counter_signal_value *val);
> > 
> > The counter_signal_value enum is simply the counter_signal_level enum
> > redefined to remove the references to the Signal data "level" data type.
> > 
> > William Breathitt Gray (3):
> >   counter: Simplify the count_read and count_write callbacks
> >   docs: driver-api: generic-counter: Update Count and Signal data types
> >   counter: Fix typo in action_get description
> > 
> >  Documentation/driver-api/generic-counter.rst | 162 +++++++++++--------
> >  drivers/counter/104-quad-8.c                 |  33 ++--
> >  drivers/counter/counter.c                    | 101 ++----------
> >  drivers/counter/ftm-quaddec.c                |  14 +-
> >  drivers/counter/stm32-lptimer-cnt.c          |   5 +-
> >  drivers/counter/stm32-timer-cnt.c            |  17 +-
> >  drivers/counter/ti-eqep.c                    |  19 +--
> >  include/linux/counter.h                      |  76 ++-------
> >  8 files changed, 144 insertions(+), 283 deletions(-)
> > 
> > 
> > base-commit: 0c3aa63a842d84990bd02622f2fa50d2bd33c652
> > prerequisite-patch-id: ebe284609b3db8d4130ea2915f7f7b185c743a70
> > prerequisite-patch-id: cbe857759f10d875690df125d18bc04f585ac7c9
> > prerequisite-patch-id: 21f2660dc88627387ee4666d08044c63dd961dae
> 

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