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Date: Thu, 13 Jan 2011 17:12:37 -0800
From: Yinghai Lu <yinghai@kernel.org>
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To: Greg KH <greg@kroah.com>
CC: Jason Wessel <jason.wessel@windriver.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Christoph Lameter <cl@linux.com>, Tejun Heo <tj@kernel.org>
Subject: Re: [RFC PATCH] x86: Add safe_udelay() and safe_msleep()
References: <AANLkTika_bZxXO3PKek+BHoYqgYGPBPER-H9KJJXjJzn@mail.gmail.com> <20110111135655.GA6901@kroah.com> <4D2CFEAD.6070206@kernel.org> <1294799565.9586.13.camel@pasglop> <4D2F7AE9.2000809@kernel.org> <20110113224450.GA14918@kroah.com> <alpine.LFD.2.00.1101132349590.2678@localhost6.localdomain6> <4D2F84FC.7000804@kernel.org> <20110113234852.GB17904@kroah.com> <4D2F9948.8000804@kernel.org> <20110114004428.GA26847@kroah.com>
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On 01/13/2011 04:44 PM, Greg KH wrote:
> On Thu, Jan 13, 2011 at 04:31:04PM -0800, Yinghai Lu wrote:
>> there are some udelay() in drivers/usb/early/ehci-dbgp.c
>>
>> that is for early USB debug port console support.
>>
>> We should replace them with early version udelay()
> 
> Again, I fail to see why.  They work fine today, right?

did not test that for a while.

from code review, we should not use udelay() that early.

in arch/x86/lib/delay.c we have
inline void __const_udelay(unsigned long xloops)
{
        int d0;

        xloops *= 4;
        asm("mull %%edx"
                :"=d" (xloops), "=&a" (d0)
                :"1" (xloops), "0"
                (this_cpu_read(cpu_info.loops_per_jiffy) * (HZ/4)));

        __delay(++xloops);
}
EXPORT_SYMBOL(__const_udelay);

that percpu cpu_info.loops_per_jiffy only have value after smp_prepare_cpus() is called.

> 
> You _really_ need to prove what you are trying to do here, with lots of
> details and descriptions of what the problem is, as it's getting a bit
> annoying...

sorry for that.

Yinghai