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

From: David Lechner <david@lechnology.com>
To: William Breathitt Gray <vilhelm.gray@gmail.com>,
	gregkh@linuxfoundation.org
Cc: jic23@kernel.org, linux-arm-kernel@lists.infradead.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-iio@vger.kernel.org, fabrice.gasnier@st.com,
	benjamin.gaignard@st.com, robh+dt@kernel.org, knaack.h@gmx.de,
	lars@metafoo.de, pmeerw@pmeerw.net, mark.rutland@arm.com
Subject: Re: [PATCH v7 00/10] Introduce the Counter subsystem
Date: Mon, 2 Jul 2018 13:13:40 -0500	[thread overview]
Message-ID: <603b0373-f1e1-5938-fa53-8328c9a5964f@lechnology.com> (raw)
In-Reply-To: <cover.1529607879.git.vilhelm.gray@gmail.com>

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