Re: [PATCH v2 1/1] counter: cros_ec: Add synchronization sensor

From: Jonathan Cameron <jonathan.cameron@huawei.com>
To: William Breathitt Gray <vilhelm.gray@gmail.com>
Cc: Jonathan Cameron <jic23@kernel.org>,
	Fabien Lahoudere <fabien.lahoudere@collabora.com>,
	<gwendal@chromium.org>, <egranata@chromium.org>,
	<kernel@collabora.com>, Jonathan Corbet <corbet@lwn.net>,
	Benson Leung <bleung@chromium.org>,
	"Enric Balletbo i Serra" <enric.balletbo@collabora.com>,
	Guenter Roeck <groeck@chromium.org>,
	Hartmut Knaack <knaack.h@gmx.de>,
	Lars-Peter Clausen <lars@metafoo.de>,
	"Peter Meerwald-Stadler" <pmeerw@pmeerw.net>,
	Lee Jones <lee.jones@linaro.org>,
	"Mauro Carvalho Chehab" <mchehab+samsung@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Nicolas Ferre <nicolas.ferre@microchip.com>,
	Nick Vaccaro <nvaccaro@chromium.org>, <linux-iio@vger.kernel.org>,
	<linux-doc@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 1/1] counter: cros_ec: Add synchronization sensor
Date: Mon, 11 Nov 2019 11:49:55 +0000	[thread overview]
Message-ID: <20191111114955.00001031@huawei.com> (raw)
In-Reply-To: <20191110151408.GB3984@icarus>

On Sun, 10 Nov 2019 10:14:08 -0500
William Breathitt Gray <vilhelm.gray@gmail.com> wrote:

> On Tue, Sep 24, 2019 at 04:20:51PM +0200, Fabien Lahoudere wrote:
> > Hi all,
> > 
> > After some discussions and investigation, the timestamp is very
> > important for that sync driver.
> > Google team uses that timestamp to compare with gyroscope timestamp.
> > 
> > So the important data is timestamp and counter value is useless.
> > Just the event of counter increment is important to get a timestamp.
> > 
> > In that case, my idea was to just use an IIO driver with a single
> > channel with IIO_TIMESTAMP. We discuss this here and it seems
> > controversial.
> > 
> > So my question to Jonathan is if we have a timestamp coming from the EC
> > itself, can we consider this timestamp as a good IIO driver?
> > 
> > Any other idea is welcome, however Google team would like to manage
> > only IIO drivers if possible.
> > 
> > Thanks  
> 
> Jonathan,
> 
> Should the the timestamp from the EC be introduced as an IIO driver
> using IIO_TIMESTAMP?

It is is a rather odd driver but I suppose it would be fine with lots
of clear docs on why it is how it is...

> 
> Since there is no corresponding EC Counter driver in the baseline right
> now we don't have a conflict yet. If the EC timestamp is introduced as
> an IIO driver then we should make any future EC Counter driver mutually
> exclusive with the IIO driver in order to prevent any memory space
> conflict. At that point we may deprecate the IIO driver and move the
> timestamp functionality to the corresponding Counter driver.

That route does become somewhat of a mess so I suspect we'd have to have
a single driver supporting both userspace interfaces.  If you are happy
that we'd be adding a bit of legacy to support for ever then we can go
that way.

> 
> That's assuming someone is interested in the Count component enough to
> implement an EC Counter driver; otherwise, the IIO driver will serve
> just fine if timestamp is the only data desired from this device.
> 
> William Breathitt Gray