linux at dominikbrodowski.de
Sat Mar 27 09:56:21 GMT 2004
On Fri, Mar 26, 2004 at 10:22:41PM +0000, Russell King wrote:
> > b) there's a config bit in the bridge which enables and/or disables the
> > forwarding of other ioport/iomem access.
> I suspect clearing the NoISA bit will be extremely dodgy. By clearing it,
> you forward all ISA accesses within the bridge windows to the subordinate
> bus instead of being forwarded to the ISA bridge.
On common x86 chipsets, the NoISA bit is even ignored: from Intel's
0 I/O Space Enable (IOSE) R/W. The ICH4 provides this bit as read/writable
for software only. However, the ICH4 ignores the programming of this bit and
runs hub interface I/O cycles to PCI that are not intended for USB, IDE, or
Also, the bridge windows are sometimes so small that there's indeed the
_need_ to clear the NoISA flag. Arjan had a patch to do this, IIRC.
> Really, it is only safe to allocate within the first 256 bytes of every
> 1K of memory on PCI buses in x86 PCs, and for PCMCIA only the lower 1K,
> provided you have full usage information for the motherboard IO ports.
Why is that?
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