linux-kernel - Re: [PATCH v2 16/16] misc: support for I-8024 in LP-8x4x

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Date:	Sun, 15 Dec 2013 03:03:51 +0400
From:	Sergei Ianovich <ynvich@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Rob Landley <rob@...dley.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v2 16/16] misc: support for I-8024 in LP-8x4x

On Sat, 2013-12-14 at 21:59 +0100, Arnd Bergmann wrote:
> Have you checked that the nsleep definition actually does the
> right thing here? 450 nanoseconds must be close the latency
> you get from calling schedule_hrtimeout(). I'd suggest using
> either ndelay() or usleep_range() instead, depending on your
> needs.

Documentation/timers/timers-howto.txt stated there was a significant
overhead when setting up usleep_range. I studied implementation and
found that schedule_hrtimeout was certainly less than 520000 CPU cycles
that udelay(1) would consume.

It worked. I haven't checked actual delay time. However, machines with
the driver (based on 3.8) are in production since May 2013 without
issues.

> If nsleep is really useful here, we should probably add that
> as a generic API rather than having it in one driver.

I've also used this nsleep for driving RTC clock (DS1302) since May
2013.

Now I see that my code is a clone of usleep_range(x, x). I will convert
my code to use it.

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