linux-kernel - Re: [PATCHv4 0/4] ARM: Fixing udelay() for SMP and non-SMP systems

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Date:	Fri, 4 Mar 2011 11:10:03 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Saravana Kannan <skannan@...eaurora.org>,
	Daniel Walker <dwalker@...eaurora.org>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	John Stultz <johnstul@...ibm.com>,
	Brian Swetland <swetland@...gle.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mattias Wallin <Mattias.Wallin@...ricsson.com>
Subject: Re: [PATCHv4 0/4] ARM: Fixing udelay() for SMP and non-SMP systems

2010/12/20 Stephen Boyd <sboyd@...eaurora.org>:

> These patches fix the udelay() issue pointed out on
> arm-lkml[1][2]. A quick recap: some SMP machines can scale
> their CPU frequencies independent of one another. loops_per_jiffy
> is calibrated globally and used in __const_udelay(). If one CPU
> is running faster than what the loops_per_jiffy is calculated
> (or scaled) for, udelay() will be incorrect and not wait long
> enough (or too long). A similar problem occurs if the cpu
> frequency is scaled during a udelay() call.

Hwt's happening to this patch set? We have applied it and
implemented a timer for the U8500.

Tested-by: Linus Walleij <linus.walleij@...aro.org>

Mattias WALLIN can probably also provide a Tested-by:
from ST-Ericsson if it helps.

Generally I think this is good and important stuff that should
be merged, will you be submitting it to Russells patch tracker
or pull request for 2.6.39?

Yours,
Linus Walleij
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