Re: [PATCH] dc395x: Fix support for highmem

[Mike Christie <mikenc@us.ibm.com>]

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.
> 

I got lost here. If you are talking about the need to kmap a sglist then 
software iscsi has it. iscsi-sfnet used to do

while (...)
	kmap()

but I fixed that (I think I need to use kmap_atomic though, is that 
correct or is it just a performance improvement - I am calling kmap from 
a thread too so). I just added kmap_atomic to open-iscsi and I believe 
pyx does something similar to the loop above.