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On 07-12-07 08:17, Rene Herman wrote: > On 07-12-07 06:54, David P. Reed wrote:> >> Pardon my ignorance, but is port 0xed really safe to push an out cycle >> at across the entire x86_64 family?> > Please do not top-post. Who knows, probably not. You just experienced > that 0x80 is apparently not safe for you and that one's the conventional > choice so it's likely that someone somewhere will have problems with > 0xed as well.> > That's why I adviced you'd test and see what blows up and suggested that > in the absence of better fixes a 0x80/0xed port choice might be able to > hang off machine types as retrievable from DMI or something. > > The better fix would probably be to simply udelay(1) but you need > calibrated timers before you can do that and some googling leads me to > believe that's why it's not today. There's also a possible issue in that > an I/O access might serve as a method of flushing forwarding buffers on > a PCI bridge but I have no idea if that's a real issue (and if it is, an > inb() should suffice as well).> >> How long must real _p pauses be in reality?> > 8 ISA bus cycles is the intended delay it seems which at a typical ISA > bus speed of 8 MHz amounts to 1 us.> >> (and who cares about what the code calls "really slow i/o").> > Paranoid programmers and those that need to delay for 4 us. > >> Why are we waiting at all? I read the comments in io_64.h, and am a >> bit mystified. Does Windoze or DOS do this magical mystery wait?> > The CMOS example at hand is the standard example. It's accessed through > an index/data register pair. You need to be sure that the RTC has > switched the correct internal register to the data register before you > poke at it or you may read/write the wrong one.> > Now, as said, I can't say I've ever in fact caught _any_ piece of > hardware with its pants down like that and needing this for actual > RTC/CMOS could as far as I'm aware be more of a left-over from The Olden > Days with a bus more or less directly tied to the 8086 than sensible for > anything on which Linux could run. Hard to test though and certainly for > generic outb_p use.> > Yes, DOS or at least many programs that ran under it did very similar > things but DOS ofcourse originated on those first PCs. > >> Anyway, the virtualization hooks in 32-bit x86 almost make it possible >> to isolate this simply - maybe - after the merge of 32/64 being >> contemplated.>>>> And anyone who knows what the chipset might be doing with the 80 port >> rather than POST codes, perhaps could contribute. Any nvidia folks >> who know what's happening under NDA? Any Phoenix BIOS types?> > It's fairly surprising that 0x80 is given you trouble. It's a very well > known legacy port. Even though it may not be all that sensible a thing > today I'd say that if your machine put anything other than an actual > integrated POST monitor on port 0x80 it in fact fucked up. This is a good thread to read: http://linux.derkeiler.com/Mailing-Lists/Kernel/2003-09/5700.html maybe you have some LPC device that gets confused by aborts on the bus as well. Rene. | ||||||||||||
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