Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64 with MCP51 laptops

Pavel Machek
2007-12-11T13:47:08Z

On Tue 2007-12-11 14:32:49, Andi Kleen wrote:
> > The LPC bus behaviour is absolutely and precisely defined. The timing of
> > the inb is defined in bus clocks which is perfect as the devices needing
> > delay are running at a fraction of busclock usually busclock/2.
> >
> > Older processors did not have a high precision timer so you couldn't
> > calibrate loop based delays for 1uS.
>
> For newer CPUs udelay() would be probably fine though. We seem
> to have several documented examples now where the bus aborts
> trigger hardware bugs, and it is always better to avoid such situations.
>
> I still think the best strategy would be to switch based on TSC
> availability. Perhaps move out*_p out of line to avoid code bloat.

Why is TSC significant? udelay() based on bogomips seems to be good
enough...?
Pavel
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