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    SubjectRe: [PATCH] x86: provide a DMI based port 0x80 I/O delay override
    On 30-12-07 10:30, Linus Torvalds wrote:

    > On Sun, 30 Dec 2007, Rene Herman wrote:

    >> This fixes "hwclock" triggered boottime hangs for a few HP/Compaq laptops
    >> and might as such be applicable to 2.6.24 still.
    >
    > It's not a regression as far as I can see (ie we've always done that port
    > 80 access for slow-down), and quite frankly, I think the code is horribly
    > ugly.

    It is indeed not a regression. Submitted it as a stop-gap measure for those
    specific afflicted machines but I guess they'll mostly be able to google up
    the problem and patch by now as well..

    > Using a DMI quirk for something like this is just not maintainable. Are we
    > going to live with doing new quirks forever? I'd rather just remove the
    > slowdown entirely (obviously that is not for 2.6.24 either, though!), and
    > drivers that then are shown to really need it could use their *own* ports.

    And yes, "elegant" it is neither. It's a bit of a pesky problem though. Port
    0x80 is a decidedly non-random port selection in so far that it's just about
    the only available port with guaranteed (in a PC sense) effects -- various
    chipsets make specific efforts to forward port 0x80 writes onto ISA due to
    its use as a POST port by the PC BIOS meaning the outb outside its bus-level
    effects also has fairly well defined timing characteristics. In practice, a
    udelay(2) is going to satisfy the delay property though -- but doesn't do
    anything for the other things the outb() does.

    The legacy PIT, PIC and DMA and KB controllers have been mentioned in this
    and previous incarnations of this same thread as hardware that in some
    implementations need the outb to function properly but ofcourse, no _sane_
    implementations do. With an arch that purports to support just about
    anything though there's some fairly justified fear, uncertainty, doubt that
    the ones to break aren't going to be found and reported quickly/easily. In
    itself, that could mean it's also not something to be overly worried about,
    but still not nice.

    With the various races in (legacy) drivers additionally an early suggestion
    by Andi Kleen to leave the outb in place for a DMI year < X (or no DMI
    available) and just do nothing for > X might in fact be justified.

    Rene.



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