linux-kernel - Re: [PATCH/RFC] iio: hi8435: do not enable all events by default

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Message-ID: <2e6019f5-94fc-bb13-f616-0c1cfe81a7db@cogentembedded.com>
Date:   Thu, 25 May 2017 08:47:47 +0300
From:   Nikita Yushchenko <nikita.yoush@...entembedded.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Sanchayan Maity <maitysanchayan@...il.com>,
        Gregor Boirie <gregor.boirie@...rot.com>,
        Matt Ranostay <mranostay@...il.com>, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org, Chris Healy <Chris.Healy@....aero>,
        Jeff White <Jeff.White@....aero>,
        Vladimir Barinov <vladimir.barinov@...entembedded.com>
Subject: Re: [PATCH/RFC] iio: hi8435: do not enable all events by default



24.05.2017 22:27, Jonathan Cameron wrote:
> On Tue, 23 May 2017 11:08:30 +0300
> Nikita Yushchenko <nikita.yoush@...entembedded.com> wrote:
> 
>> Having all events enabled by default is misleading.
>> Userspace should explicitly enable events they want to receive.
>>
>> Signed-off-by: Nikita Yushchenko <nikita.yoush@...entembedded.com>
> I agree in principle, but this is a userspace ABI change.  Sadly we
> can't do it with out risking breaking userspace code...
> 
> One of those we should have caught in review, but now it's there
> we can't actually do anything about it unless we are absolutely
> sure no one will notice!

I see your point.

Still, isn't there subsystem-level default that all events are disabled
by default?  If such, then current hi8435 state breaks subsystem-level
rules, which is a [userspace-visible] bug.  I'm not sure how far should
we go in bug compatibility.

One crazy idea could be - make default selectable via device tree (with
default set to all-enabled to keep bug-compatibility).  But perhaps
that's over-reaction.