Re: [PATCH 2/4] x86-64: Calgary IOMMU - move valid_dma_directioninto the callers

[Jeff Garzik]

Jon Mason wrote:
> > From Andi Kleen's comments on the original Calgary patch, move
> valid_dma_direction into the calling functions.
>
> Signed-off-by: Muli Ben-Yehuda <muli@xxxxxxxxxx>
> Signed-off-by: Jon Mason <jdmason@xxxxxxxxxx>

Even though BUG_ON() includes unlikely(), this introduces additional 
tests in very hot paths.

_Why_ do we need this at all?

I would prefer to NAK the patch, and fix the odd user that gets it 
wrong.  It becomes REALLY obvious that a driver has gotten this wrong, 
REALLY quickly.

I see no need to burden critical hot paths with dumb checks like this.

	Jeff



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