linux-kernel - Re: [PATCH v4 1/4] drivers: hwspinlock: add framework

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Date:	Mon, 31 Jan 2011 22:38:59 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ohad Ben-Cohen <ohad@...ery.com>
Cc:	linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, Greg KH <greg@...ah.com>,
	Tony Lindgren <tony@...mide.com>,
	Benoit Cousson <b-cousson@...com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Suman Anna <s-anna@...com>, Kevin Hilman <khilman@...com>,
	Arnd Bergmann <arnd@...db.de>, Paul Walmsley <paul@...an.com>,
	Hari Kanigeri <hari.kanigeri@...il.com>,
	Simon Que <simonque@...il.com>,
	Russell King <rmk@....linux.org.uk>
Subject: Re: [PATCH v4 1/4] drivers: hwspinlock: add framework

On Tue, 1 Feb 2011 08:20:13 +0200 Ohad Ben-Cohen <ohad@...ery.com> wrote:

> On Tue, Feb 1, 2011 at 1:38 AM, Andrew Morton <akpm@...ux-foundation.org> wrote:
> > It's a little irritating having two hwspinlock.h's.
> > hwspinlock_internal.h wold be a conventional approach. __But it's not a
> > big deal.
> ...
> 
> >> +/**
> >> + * __hwspin_lock_timeout() - lock an hwspinlock with timeout limit
> >> + * @hwlock: the hwspinlock to be locked
> >> + * @timeout: timeout value in jiffies
> >
> > hm, why in jiffies?
> >
> > The problem here is that lazy programmers will use
> >
> > __ __ __ __hwspin_lock_timeout(lock, 10, ...)
> >
> > and their code will work happily with HZ=100 but will explode with HZ=1000.
> >
> > IOW, this interface *requires* that all callers perform a
> > seconds-to-jiffies conversion before calling hwspin_lock_timeout(). __So
> > why not reduce their effort and their ability to make mistakes by
> > defining the API to take seconds?
> 
> I considered that, but then decided to use jiffies in order to be
> consistent with wait_event_timeout/schedule_timeout (although I don't
> return the remaining jiffies in case the lock is taken before the
> timeout elapses), and also to allow user-selected granularity.
> 
> But I do kind of like the idea of not using jiffies. We can probably
> even move to msecs, since anyway this is an error condition, and
> people who needs a quick check should just use the trylock() version.
> 
> I'll do a quick respin of the patches with that and the
> hwspinlock_internal.h comment above.

OK..

The patch series looks OK to me.  But there isn't a lot of point in me
putting them into my tree.  Maybe Tony or Russell or Greg can grab them
if they like the look of it all?

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