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    SubjectRe: [RFC PATCH] x86: Add safe_udelay() and safe_msleep()
    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


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