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SubjectRe: [patch] block-highmem-all-18
On Fri, Nov 16 2001, David S. Miller wrote:
> From: Gérard Roudier <>
> Date: Fri, 16 Nov 2001 19:59:02 +0100 (CET)
> On Fri, 16 Nov 2001, Jens Axboe wrote:
> > - Add sym2 can_dma_32 flag (me)
> ^^^^^^^^^^ Pooaaahhh!:) What's this utter oddity ?
> Only dma 32 ? :-)
> It is workaround for buggy drivers, when set it means that single SG
> list entry request will be handled correctly. When clear it means
> that single entry SG lists are to be avoided by the block layer.
> Many devices would explode when given single entry scatterlist. :(
> It's naming is questionable... that I agree with. The name should be
> more suggestive to what it really means.

Heh, actually Dave the single_sg_ok flag used to specify just that, but
Arjan noted that we never needed to trust that functionality when
!can_dma_32. So now can_dma_32 being set implies that the HBA driver
also gets the single sg entry correct.

To answer Gerard's question -- with can_dma_32 set, scsi_merge will set
the correct bounce value based on the PCI device DMA mask set. So dma_32
is indeed a misnomer, it was introduced before we supported full 64-bit
dma, and should now just be called can_highmem_io or something similar.

Jens Axboe

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