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    SubjectRe: Opinion on ordering of writel vs. stores to RAM
    On Sunday 10 September 2006 19:19, Jesse Barnes wrote:
    > On Saturday, September 09, 2006 8:09 am, Alan Cox wrote:
    > > Ar Sad, 2006-09-09 am 17:23 +1000, ysgrifennodd Benjamin
    > Herrenschmidt:
    > > > The problem is that very few people have any clear idea of what
    > > > mmiowb is :) In fact, what you described is not the definition of
    > > > mmiowb according to Jesse
    > >
    > > Some of us talked a little about this at Linux Kongress and one
    > > suggestion so people did understand it was
    > >
    > > spin_lock_io();
    > > spin_unlock_io();
    > >
    > > so that it can be expressed not as a weird barrier op but as part of
    > > the locking.
    > That's what IRIX had. It would let us get rid of mmiowb and avoid doing
    > a full sync in writeX, so may be the best option.

    Last time I suggested that, people did not want it.
    Probably about 9 months ago. Don't remember exactly.
    We came to the decision that if a driver depends on some weak
    ordering, it should either directly use mmiowb() or have its
    own locking wrapper which wraps spin_unlock() and mmiowb().

    There is one little problem in practice with something
    like spin_unlock_io().

    foovalue = new_foovalue;
    if (device_is_fooing)
    writel(foovalue, REGISTER);

    That would be an unneccessary sync in case device is not fooing.
    In contrast to the explicit version:

    foovalue = new_foovalue;
    if (device_is_fooing) {
    writel(foovalue, REGISTER);

    Greetings Michael.
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      Last update: 2006-09-10 19:39    [W:0.022 / U:44.936 seconds]
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