[PATCH v7 01/10] counter: Introduce the Generic Counter interface

On Tue, Jul 17, 2018 at 08:49:54PM -0700, Andrew Morton wrote:

On Thu, 21 Jun 2018 17:07:08 -0400 William Breathitt Gray [off-list ref] wrote:

quoted

This patch introduces the Generic Counter interface for supporting
counter devices.

+EXPORT_SYMBOL(count_direction_str);
+EXPORT_SYMBOL(count_mode_str);
+EXPORT_SYMBOL(counter_signal_enum_read);
+EXPORT_SYMBOL(counter_signal_enum_write);
+EXPORT_SYMBOL(counter_signal_enum_available_read);
+EXPORT_SYMBOL(counter_count_enum_read);
+EXPORT_SYMBOL(counter_count_enum_write);
+EXPORT_SYMBOL(counter_count_enum_available_read);
+EXPORT_SYMBOL(counter_device_enum_read);
+EXPORT_SYMBOL(counter_device_enum_write);
+EXPORT_SYMBOL(counter_device_enum_available_read);
+EXPORT_SYMBOL(signal_read_value_set);
+EXPORT_SYMBOL(count_read_value_set);
+EXPORT_SYMBOL(count_write_value_get);
+EXPORT_SYMBOL(counter_register);
+EXPORT_SYMBOL(counter_unregister);
+EXPORT_SYMBOL(devm_counter_register);
+EXPORT_SYMBOL(devm_counter_unregister);

The naming is a bit chaotic.  Most of the symbols start with counter_,
which is good.  But a handful do not.

I can prefix these exported symbols with "counter_" to help make it
clear they all belong to the Generic Counter API. I'll keep the devm_*
symbols the same to match the naming convention in the other subsystems
I see (watchdog, IIO, GPIO, etc.).

Also, symbols called signal_* make my head spin - Linux already has a
firmly ingrained notion of what a signal is, and this ain't it ;)
Although the kernel tends to use sig_ for signals-as-an-IPC-thing.

Also, many many drivers deal with signals-as-an-electrical-thing - is
it appropriate for this particular driver to take that namespace?

In the context of the Generic Counter paradigm, a "Signal" is an
abstraction for the stream of data that is fed to the counter device for
evaluation (triggering updates for the readable "Count"). In many cases
a "Signal" correlates with a physical electrical line (for example the A
and B electrical lines for a quadrature encoder), but this isn't a hard
requirement as the paradigm permits more abstract data streams.

I decided on "Signal" to match the naming convention that appears in the
datasheets of many counter devices, but "Line" may be a decent
alternative name we could use to indicate a counter device input data
stream.

I'd like to get some other opinions as well before I make a naming
change to "Signal" -- whether to stay with "Signal," switch to "Line," or
rename to something else. For what it's worth, I think it's unlikely for
a counter device driver author to confuse a Counter Signal with the
Linux OS signal within the context of the Generic Counter paradigm and
their respective counter device datasheet.

William Breathitt Gray