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

Pavel Machek
2007-12-09T13:10:49Z

Hi!

> > modern CPU compared to the bus. But the delay really needs to be something
> > that is about IO port speed. Ok in theory you could try to measure
> > a outb using RDTSC and then use udelay, but first you would need
>
> You don't need to. Port 0x80 historically is about 8uS so just udelay(8)
> and make sure the initial default delay is conservative enough before the
> CPU speed is computed.
>
> 0x80 should be fine for anything PC compatible anyway, its specifically
> reserved as a debug port and supported for *exactly* that purpose by
> many chipsets.

Actually, I've seen few pci cards with leds on port 0x80, and I
wonder: is our outb_p really correct?

I mean, we expect 8usec delay -- historical ISA timing -- but when
_PCI_ card with leds is inserted, it is likely to be faster than old
ISA, right?
Pavel
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