Re: pci resource mapping problem for PCI-X mode

From: David S. Miller (
Date: Fri Jul 20 2001 - 18:54:15 EST

Raj, Ashok writes:
> it works for now, since the addr msb's are 0. but if this physical addr is a
> true 64bit addr
> the above wont work..

On a 32-bit system, the BIOS (nor the kernel) will never assign a
resource to the device with the upper 32-bits non-zero.

This is also done for compatability reasons, so that PCI devices which
may only perform SAC transactions (ie. no dual-address cycle
capability) may do PCI peer-to-peer DMA to/from devices even when
using 64-bit BARs.

To be honest, 64-bit BARs are pretty useless today, being that %99 of
PCI controllers do not even provide a way for the cpu to address the
PCI memory space above 4GB. This is true even on 64-bit CPU systems.

In short there are no problems.

David S. Miller

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This archive was generated by hypermail 2b29 : Mon Jul 23 2001 - 21:00:14 EST