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

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Message-ID: <20170528164846.3fa3d4d8@kernel.org>
Date:   Sun, 28 May 2017 16:48:46 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Nikita Yushchenko <nikita.yoush@...entembedded.com>
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

On Thu, 25 May 2017 08:47:47 +0300
Nikita Yushchenko <nikita.yoush@...entembedded.com> wrote:

> 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.
It is indeed the subsystem default (as much as we have one)

This is a moderately obscure chip for linux systems, do we have a good handle
on where it is being used - i.e. are most of the devices under control of
people we can discuss this with?
> 
> 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.
Yeah, wouldn't fly with the devicetree binding maintainers..

Jonathan