linux-kernel - Re: [PATCH v2 1/3] iio: light: Add driver for ap3216c

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Message-ID: <CAGngYiW0Sf1mg-F18p_NeJZUMsvvceRn4HvNXAkdLaS9AfFDMQ@mail.gmail.com>
Date:   Mon, 4 Mar 2019 11:25:01 -0500
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Robert Eshleman <bobbyeshleman@...il.com>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-iio@...r.kernel.org
Subject: Re: [PATCH v2 1/3] iio: light: Add driver for ap3216c

On Sun, Mar 3, 2019 at 9:38 AM Jonathan Cameron <jic23@...nel.org> wrote:
>
> Hmm. Just been thinking a bit about the events on here and wondered
> if it is possible to mask them through careful use of the threshold
> values - i.e. can we stop the hardware generating the interrupts for
> the ones we don't want. It would be unusual for hardware to be
> designed where this wasn't possible.

Excellent point! People with power / battery constraints take a dim view of
receiving interrupts when no-one wants them. So disabling them in h/w
is definitely the way to go, if possible.

And yes, this also makes a non-issue of thresh_en visibility concerns, if any.

>
> Alternatively if you have a scope or equivalent to verify if it is doing
> these as a multi byte read and working that would be even better.
> It is not uncommon for hardware to implement fairly standard i2c features
> like this and not document them because they weren't what the test code
> the docs writer got given does! (may not be true here of course)

Or alternatively, the current chip rev supports undocumented multi-reads,
and the next revision silently drops support, thereby breaking the driver...
Been there, done that, got the T-shirt :(