linux-kernel - Re: [PATCH 0/4] Introduce the Counter character device interface

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Date:   Wed, 29 Apr 2020 15:21:05 -0500
From:   David Lechner <david@...hnology.com>
To:     William Breathitt Gray <vilhelm.gray@...il.com>, jic23@...nel.org
Cc:     kamel.bouhara@...tlin.com, gwendal@...omium.org,
        alexandre.belloni@...tlin.com, felipe.balbi@...ux.intel.com,
        fabien.lahoudere@...labora.com, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, syednwaris@...il.com,
        patrick.havelange@...ensium.com, fabrice.gasnier@...com,
        mcoquelin.stm32@...il.com, alexandre.torgue@...com
Subject: Re: [PATCH 0/4] Introduce the Counter character device interface

On 4/29/20 1:11 PM, William Breathitt Gray wrote:
> Over the past couple years we have noticed some shortcomings with the
> Counter sysfs interface. Although useful in the majority of situations,
> there are certain use-cases where interacting through sysfs attributes
> can become cumbersome and inefficient. A desire to support more advanced
> functionality such as timestamps, multi-axis positioning tables, and
> other such latency-sensitive applications, has motivated a reevaluation
> of the Counter subsystem. I believe a character device interface will be
> helpful for this more niche area of counter device use.

Nice to see some progress being made. :-)

> 
> Interaction with Counter character devices occurs via ioctl commands.
> This allows userspace applications to access and set counter data using
> native C datatypes rather than working through string translations.

For most aspects of the counter subsystem, this is not an issue since
configuring a counter is not a time-sensitive operation. Instead of
ioctls, I was expecting to just be able to read the character device
and receive counter events or poll to wait for events similar to how
the input subsystem works or how buffers work in the iio subsystem.

I'm afraid I don't really see much use in having ioctls that do
exactly what sysfs already does. And my intuition tells me that the
extra work needed to maintain it will probably cost more than any
benefit gained. (Maybe other have a different experience that leads
to a different conclusion?)