linux-kernel - Re: [PATCH v5 2/3] i2c: iproc: Add Broadcom iProc I2C Driver

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Message-ID: <20150118115650.GH22880@pengutronix.de>
Date:	Sun, 18 Jan 2015 12:56:51 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Arend van Spriel <arend@...adcom.com>
Cc:	Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Florian Fainelli <f.fainelli@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Pawel Moll <pawel.moll@....com>,
	Scott Branden <sbranden@...adcom.com>,
	Wolfram Sang <wsa@...-dreams.de>, Ray Jui <rjui@...adcom.com>,
	Christian Daudt <bcm@...thebug.org>,
	linux-kernel@...r.kernel.org, Matt Porter <mporter@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	bcm-kernel-feedback-list@...adcom.com, linux-i2c@...r.kernel.org,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 2/3] i2c: iproc: Add Broadcom iProc I2C Driver

Hello,

On Sun, Jan 18, 2015 at 12:46:51PM +0100, Arend van Spriel wrote:
> On 01/18/15 12:17, Uwe Kleine-König wrote:
> >Hello Wolfram,
> >
> >On Sun, Jan 18, 2015 at 12:06:58PM +0100, Wolfram Sang wrote:
> >>On Sun, Jan 18, 2015 at 10:47:41AM +0100, Uwe Kleine-König wrote:
> >>>On Sun, Jan 18, 2015 at 10:14:04AM +0100, Arend van Spriel wrote:
> >>>>On 01/17/15 00:42, Ray Jui wrote:
> >>>>>+	complete_all(&iproc_i2c->done);
> >>>>
> >>>>Looking over this code it seems to me there is always a single
> >>>>process waiting for iproc_i2c->done to complete. So using complete()
> >>>>here would suffice.
> >>>Yeah, there is always only a single thread waiting. That means both
> >>>complete and complete_all are suitable. AFAIK there is no reason to pick
> >>>one over the other in this case.
> >>
> >>Clarity?
> >And which do you consider more clear? complete_all might result in the
> >question: "Is there>1 waiter?" and complete might yield to "What about
> >the other waiters?". If you already know there is only one, both are on
> >par on clarity. Might only be me?! I don't care much.
> 
> Maybe it is me, but it is not about questions but it is about
> implicit statements that the code makes (or reader derives from it).
> When using complete_all you indicate to the reader "there can be
> more than one waiter". When using complete it indicates "there is
> only one waiter". If those statements are not true that is a code
No, complete works just fine in the presence of >1 waiter. It just wakes
a single waiter and all others continue to wait.
That is, for single-waiter situations there is no semantic difference
between complete and complete_all. But there is a difference for
multi-waiter queues.

I think this is just a matter of your POV in the single-waiter
situation: complete might be intuitive because you just completed a
single task and complete_all might be intuitive because it signals
"I'm completely done, there is noone waiting for me any more.".

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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