linux-kernel - Re: [PATCH v7 00/10] Introduce the Counter subsystem

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Date:   Mon, 2 Jul 2018 13:13:40 -0500
From:   David Lechner <david@...hnology.com>
To:     William Breathitt Gray <vilhelm.gray@...il.com>,
        gregkh@...uxfoundation.org
Cc:     jic23@...nel.org, linux-arm-kernel@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-iio@...r.kernel.org, fabrice.gasnier@...com,
        benjamin.gaignard@...com, robh+dt@...nel.org, knaack.h@....de,
        lars@...afoo.de, pmeerw@...erw.net, mark.rutland@....com
Subject: Re: [PATCH v7 00/10] Introduce the Counter subsystem

On 06/21/2018 04:06 PM, William Breathitt Gray wrote:
> I decided to strip down these devices to arrive at the core essence of
> what constitutes a "counter device" and therefore design a "generic
> counter" abstraction to better represent these devices and prevent the
> ambiguity we discovered with the existing IIO Counter interface. This
> abstraction became the Generic Counter paradigm, which is explained in
> detail within the Documentation/driver-api/generic-counter.rst file
> introduced by this patchset.

I'm curious if you have given any thought to the time aspect of counters.
I am interested in the rate at which the counters are counting (e.g. how
many counts per second). I realize that you can calculate this in
userspace or in the kernel using the system timer, but it is not very
accurate since Linux is not a realtime OS. So, I would like to get the
rate directly from the hardware. For example, the TI eQEP[1], like the
one found in BeagleBones, has a couple ways of measuring time (see link
for details).

[1]: http://www.ti.com/lit/ug/sprug05a/sprug05a.pdf