linux-kernel - Re: [PATCH v5 1/3] clocksource: timer-keystone: introduce clocksource driver for Keystone

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Message-ID: <52F3975B.2080806@ti.com>
Date:	Thu, 6 Feb 2014 16:08:27 +0200
From:	Ivan Khoronzhuk <ivan.khoronzhuk@...com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	<santosh.shilimkar@...com>, <rob@...dley.net>,
	<linux@....linux.org.uk>, <galak@...eaurora.org>,
	<robh+dt@...nel.org>, <pawel.moll@....com>, <mark.rutland@....com>,
	<ijc+devicetree@...lion.org.uk>, <daniel.lezcano@...aro.org>,
	<devicetree@...r.kernel.org>, <linux-doc@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <grygorii.strashko@...com>
Subject: Re: [PATCH v5 1/3] clocksource: timer-keystone: introduce clocksource
 driver for Keystone


On 02/05/2014 10:27 PM, Thomas Gleixner wrote:
> On Wed, 5 Feb 2014, Ivan Khoronzhuk wrote:
>> +	/* here we have to be sure the timer has been disabled */
> Sigh. This is not a proper explanation for a barrier, really. You want
> to explain what it serializes against what. i.e. you want to explain
> why you are using the relaxed functions and avoid a separate non
> relaxed variant in favour of an explicit barrier.
>
>> +	__iowmb();
> The proper thing is to have an inline function key_stone_barrier() and
> a full explanation of the issue in exactly that place instead of
> handwaving comments here and there.
>
> Thanks,
>
> 	tglx

I can add new inline function like:

/**
  * keystone_timer_barrier: write memory barrier
  * use explicit barrier to avoid using readl/writel non relaxed function
  * variants, because in our case relaxed variants hide the true places
  * where barrier is needed.
  */
static inline void keystone_timer_barrier(void)
{
     __iowmb();
}

and use it where it is needed.
Are you OK with it?

And I propose to leave comments under the barriers in order to be
able to understand why they are used.

-- 
Regards,
Ivan Khoronzhuk

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