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Highmem SCSI driver

We are trying to test 64-bit PCI DMA for a SCSI driver on a Xeon box,

RH9 2.4.20-8 bigmem kernel, 6GB RAM.
The machine shows 6GB in top, we set highmem_io in the driver, PCI DMA 
mask covers 64-bit range, etc.

Of course we're trying to make sure that the system does not create 
bounce buffers unnecessarily. On a 64-bit box (AMD64) everything works 
as expected. On the Xeon, no matter what we try, we never see I/Os 
mapped above 4GB.

Any ideas on how we can drive I/Os mapped above 4GB down to our driver?

Thanks,
-Mark



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