linux-kernel - Re: [PATCH v3) posix-timers: make it configurable

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Message-ID: <20160915215649.GA17171@cloud>
Date:   Thu, 15 Sep 2016 14:56:49 -0700
From:   Josh Triplett <josh@...htriplett.org>
To:     Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:     Richard Cochran <richardcochran@...il.com>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3) posix-timers: make it configurable

On Thu, Sep 15, 2016 at 05:35:28PM -0400, Nicolas Pitre wrote:
> On Thu, 15 Sep 2016, Josh Triplett wrote:
> 
> > On Thu, Sep 15, 2016 at 11:07:24PM +0200, Richard Cochran wrote:
> > > On Thu, Sep 15, 2016 at 12:58:22PM -0700, John Stultz wrote:
> > > > This doesn't look too bad.
> > > 
> > > I disagree.  It looks ugly.  If tinification means sprinkling more and
> > > more of these conditionals all over the place, then it is going to be
> > > a tough sell.
> > 
> > Looking at this particular patch, it does seem a bit much for the
> > ability to have PTP without timers.  That doesn't seem like a very
> > likely combination.  Handling that in Kconfig seems fine, unless there's
> > a concrete use case for that combination.
> 
> I doubt there is.  This is more for randconfig purposes or the like.
> 
> I suspect there is more of a case for having net drivers _without_ ptp 
> support.  This could be implemented with a ptp_clock_register() stub 
> returning NULL when ptp is not configured.  I didn't look at most 
> drivers but at least broadcom/tg3.c seems to be fine with such an 
> approach.
> 
> Alternatively, all those ethernet drivers currently selecting 
> PTP_1588_CLOCK could be banned from the kernel config when POSIX_TIMERS 
> is not selected.
> 
> What do people prefer?

If the stubs prove as simple as you suggest above (a static inline
returning NULL), that sounds ideal.  If this would require a non-trivial
amount of stub code, then preventing those drivers from building without
POSIX_TIMERS seems preferable to that.