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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