Re: [PATCH] dc395x: Fix support for highmem

[Christoph Hellwig <hch@infradead.org>]

On Wed, Mar 16, 2005 at 06:04:17PM +0100, Jens Axboe wrote:
> On Wed, Mar 16 2005, Christoph Hellwig wrote:
> > On Wed, Mar 16, 2005 at 05:53:39PM +0100, Jens Axboe wrote:
> > > The list doesn't really need dma mapping at that point, the problem here
> > > is that the driver needs to punt to pio mode because of foo. So calling
> > > pci/dma_map_* is pointless, since the CPU will have to do the transfer
> > > anyways. What the driver is really looking for at this point, is a way
> > > to map the pages in the sglist to a virtual address.
> > 
> > Given that there's quite a few cases of this "problem" it would be nice
> > to have common helpers for it.  Especially as it's really difficult when
> > we allow merging of sg list entries
> 
> I thought about that when writing the above, but is there really more
> than one case for SCSI drivers? If there is, sure lets add the helpers.
> But I would consider it a quite rare occurence, I've never seen it
> before.

There's lots of pio only drivers, aswell as raid drivers that need to
look into the non I/O-path command and things like iscsi.