linux-kernel - Re: [PATCH v2] clocksource: exynos-mct: Register the timer for stable udelay

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Date:	Thu, 19 Jun 2014 12:29:55 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	amit daniel kachhap <amit.daniel@...sung.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	David Riley <davidriley@...omium.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Doug Anderson <dianders@...omium.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tomasz Figa <tomasz.figa@...il.com>
Subject: Re: [PATCH v2] clocksource: exynos-mct: Register the timer for stable udelay

On Thursday 19 June 2014 15:51:58 amit daniel kachhap wrote:
> I also didn't want to use macros but used as a last option. you want
> me to put more comments here?
> Or something like below is also possible for checking the size of
> (unsigned long) in runtime.
> 
> unsigned long x;
> unsigned int size = (char *)(&x + 1) - (char *)(&x);

reimplementing "sizeof (long)"?

> if (size == 4)
>            return __raw_readl(reg_base + EXYNOS4_MCT_G_CNT_L);

readl_relaxed(), certainly

> else
>            return exynos4_frc_read(&mct_frc);
> 
> But this involves extra computation which should not be used for time
> critical functions.

sizeof is a constant expression, the compiler will optimize this.

	Arnd
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