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

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Date:   Sat, 3 Aug 2019 01:40:45 +0900
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     David Lechner <david@...hnology.com>
Cc:     linux-iio@...r.kernel.org, linux-omap@...r.kernel.org,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Benoît Cousson <bcousson@...libre.com>,
        Tony Lindgren <tony@...mide.com>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org
Subject: Re: [PATCH 2/4] counter: new TI eQEP driver

On Fri, Aug 02, 2019 at 11:17:11AM -0500, David Lechner wrote:
> 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.

All right, in that case you can ignore signal_read.

> > 
> > 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.

That should be fine for now. We can add them in a later patch down the
road and keep this introduction patch simple.

William Breathitt Gray