Re: libata+SGIO: is .dma_boundary respected?

[Mark Lord <liml@rtr.ca>]

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.