linux-kernel - clock_getres() and real resolution

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Message-ID: <4F32A347.4090703@linaro.org>
Date:	Wed, 08 Feb 2012 08:31:03 -0800
From:	Dmitry Antipov <dmitry.antipov@...aro.org>
To:	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>
CC:	linux-kernel@...r.kernel.org, linaro-dev@...ts.linaro.org
Subject: clock_getres() and real resolution

IIUC, an idea behind clock_getres() is to give a hint about the resolution of
specified clock. This hint may be used by an application programmer to check whether
this clock is suitable for a some purpose. So why clock_getres() always returns
something like {0, 1} (if hrtimers are enabled) regardless of the underlying platform's
real numbers?

For example, OMAP4's real resolution of CLOCK_REALTIME is 30.5us for 32K timer and 26ns
for MPU timer. Such a difference definitely makes sense - but clock_getres(CLOCK_REALTIME,..)
always returns {0, KTIME_HIGH_RES}. Since this behavior causes a confusion like
http://lists.linaro.org/pipermail/linaro-dev/2012-February/010112.html, I'm considering
this as a stupid misfeature.

Dmitry
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