Mark Lord wrote:
Jeff Garzik wrote:
The idiot IOMMU layer may merge too aggressively, which is the reason
for this code and similar code in ata_fill_sg(). The IOMMU stuff
always happens at pci_map_sg() time, after the block layer gets out of
the way.
Ahh.. then how does the low-level driver know what to use for
".sg_tablesize"?
It cannot use the real hardware/driver value, because it may need to do
request splitting. I wonder what the worst case number of splits required
is, for each sg[] entry?
Mmmm. I suppose the answer is that the block layer guarantees
no more than .sg_tablesize entries, and the IOMMU layer may reduce
the segment count, but never increase it.
So the low-level driver should be able to safely use it's own internal
hardware/driver limit when registering .sg_tablesize.
Mmm.. sata_mv.c currently divides by two.
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