Date: Thu, 22 Jun 2017 22:54:00 -0700
From: Darren Hart <dvhart@infradead.org>
To: Jonathan Woithe <jwoithe@just42.net>
Cc: Micha?? K??pie?? <kernel@kempniu.pl>,
        Rafael Wysocki <rjw@rjwysocki.net>,
        Andy Shevchenko <andy@infradead.org>,
        platform-driver-x86@vger.kernel.org, linux-acpi@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/7] platform/x86: fujitsu-laptop: do not use kfifo for
 storing hotkey scancodes
Message-ID: <20170623055400.GE27213@fury>
References: <20170616044058.30443-1-kernel@kempniu.pl>
 <20170616044058.30443-2-kernel@kempniu.pl>
 <20170621181543.GB25900@fury>
 <20170621235021.GA32131@marvin.atrad.com.au>
 <20170622024413.GE25900@fury>
 <20170622030120.GF32131@marvin.atrad.com.au>
 <20170622204619.GB4194@kmp-mobile.hq.kempniu.pl>
 <20170622235809.GB27213@fury>
 <20170623001458.GE24368@marvin.atrad.com.au>
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On Fri, Jun 23, 2017 at 09:44:58AM +0930, Jonathan Woithe wrote:
> On Thu, Jun 22, 2017 at 04:58:09PM -0700, Darren Hart wrote:
> > On Thu, Jun 22, 2017 at 10:46:19PM +0200, Micha?? K??pie?? wrote:
> > > > The events seen by userspace with the original code would be "A-press",
> > > > "B-press", "A-release", "B-release".  With the revised code the order of the
> > > > release events would be reversed compared to the previous behaviour.  That
> > > > is, unless I've misunderstood how sparse_keymap_report_event() works.
> > > 
> > > All you wrote above is correct and this patch does change the order of
> > > release events sent to userspace when multiple hotkeys are pressed
> > > simultaneously.  The question is: is it relevant for any practical
> > > scenario?
> > > 
> > > Anyway, I find this matter to be of secondary importance.  The primary
> > > objective of this patch is to get rid of the kfifo.  If anyone has
> > > strong feelings about the change in event ordering, I will be happy to
> > > revert to FIFO in v2.
> > 
> > This all looks reasonable to me, I don't see anything requiring a respin.
> 
> I agree it is of seconary importance.  To me, using LIFO release order is
> counter-intuitive, but it's the sort of question that if put to 100 people
> you'll get a 50/50 split of opinions.
> 
> Especially since the whole "multiple buttons held at once" scenario is
> rather unusual we can go with switching the order if others don't see a
> problem with the behavioural change.

Yes. If anyone notices the implementation difference, I'll be rather surprised.
If they do, we can convert back to FIFO as you say.
-- 
Darren Hart
VMware Open Source Technology Center