Re: [PATCH 2/4] counter: new TI eQEP driver

From: David Lechner
Date: Fri Aug 02 2019 - 12:17:19 EST

On 8/2/19 4:27 AM, William Breathitt Gray wrote:
+static const struct counter_ops ti_eqep_counter_ops = {
+ .count_read = ti_eqep_count_read,
+ .count_write = ti_eqep_count_write,
+ .function_get = ti_eqep_function_get,
+ .function_set = ti_eqep_function_set,
Are you able to provide a signal_read function, or are the Signals not
exposed to the user by this device? Sometimes quadrature encoder devices
provide an instanteous read of the signal lines to tell whether they are
high or low, so I figured I'd ask.

No, it does not look like these signals can be read directly.

You should define an action_get function as well along with Synapses
corresponding to each Signal. This will allow users to know whether the
Synapse fires on a rising edge, falling edge, no edge, or both edges.

For example, consider the drivers/counter/104-quad-8.c file. Each count
register has three associated signal lines: Quadrature A, Quadrature B,
and Index.

Quadrature A and B are your typical quadrature encoder lines and
depending on the function mode selected (quadrature x4, pulse-direction,
etc.) could have a Synapse action mode of none, rising edge, falling
edge, or both edges; see the quad8_synapse_actions_list array.

In contrast, the Index signal line only has two Synapse action modes:
rising edge (in the case preset functionality is enabled) or none.

The encoders I have don't use the index or strobe signals, so I was
thinking maybe I should omit those two signals from the driver for the
time being since I don't have a way of testing.

For the TI eQEP driver, there will be four Synapses corresponding to the
four Signals: QEPA, QEPB, QEPI, and QEPS. See if you are able to
implement the Synapses and action_get function by using the 104-quad-8.c
file as a reference. That file does have a lot of extra functionality
tossed in compared to yours, so if you have trouble groking it, just let
me know and I'll try to help.