Messages in this thread |  | | Date | Fri, 16 Nov 2001 23:45:55 +0100 | From | Jens Axboe <> | Subject | Re: [patch] block-highmem-all-18 |
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On Fri, Nov 16 2001, David S. Miller wrote: > From: Gérard Roudier <groudier@free.fr> > 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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