Re: [PATCH] x86: provide a DMI based port 0x80 I/O delay override.

[Rene Herman]

On 02-01-08 00:11, Rene Herman wrote:

> On 01-01-08 23:39, H. Peter Anvin wrote:
>
> > > > Yes, we do.  It's exactly this side effect which makes this safer 
> > > > than either 0x80 or 0xED -- it's a port that *guaranteed* can't be 
> > > > reclaimed for other purposes without breaking MS-DOS compatibility.
> > >
> > > I see that with CR0.NE set (*) we indeed don't care about IGNNE#...
> > >
> > > However, I'm worried about this comment in arch/x86/kernel/i8259_32.c
> > >
> > > ===
> > > /*
> > >  * New motherboards sometimes make IRQ 13 be a PCI interrupt,
> > >  * so allow interrupt sharing.
> > >  */
> > > ===
> > >
> > > Is it really safe to just blindly negate IRQ13 on everything out 
> > > there, from regular PC through funky embedded thingies?
> >
> > It's not any IRQ 13, it's IRQ 13 from the FPU.
>
> Well, on the PIIX it is and I guess on anything where it's _not_ fully 
> internal an 0xf0 write wouldn't have any effect on IRQ13...
>
> When you earlier mentioned this it seemed 0xed switched on DMI would be 
> good enough, but well.
>
> Alan, do you have an opinion on the port 0xf0 write? It should probably 
> still be combined with a replacement/deletion for new machines due to 
> the bus-locking "bad for real-time" thing you mentioned earlier but in 
> the short run it could be a fairly low-impact replacement on anything 
> except a 386+387
>
> We should do a another timing measurement survey and it makes for 
> sligtly worse code if we indeed feel it's not safe enough to write 
> anything other than 0, but otherwise it's quite minimal.

Thinking about this, my main worry about 0xf0 as a 0x80 replacement would be 
systems that have elected to _not_ let port 0xf0 writes flow through to ISA 
changing the timing-characteristics. Given that it's a known port, someone 
may have elected to just keep it fully internal.

Upto now the datasheets I've read do put it on ISA...

Rene.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/