[openib-general] [PATCH v2 1/7] IB/core - Add DMA mapping functions to allow device drivers to interpose

[Or Gerlitz]

On 11/30/06, Ralph Campbell <ralph.campbell at qlogic.com> wrote:
> On Thu, 2006-11-30 at 12:10 -0800, Roland Dreier wrote:
> > So what did you change since v1?  How do you deal with fitting 64-bit
> > addresses into an sg list entry that has a 32-bit dma_addr_t?

> The ipath_map_sg() handler for ib_dma_map_sg() doesn't store
> anything in the struct scatterlist.  The translation is
> done when ipath_sg_dma_address() is called which now
> returns u64 instead of dma_addr_t thus avoiding the truncation
> problem.

And there is this open/TODO of calling kmap(page) on dma mapping time
(or when ipath_sg_dma_address is called) and kunmap(page) on dma
unmapping time, where you must store the kvaddr between the two calls
and the sg does not have a room for it where dma_addr_t is u32 and
kvaddr is u64 ....

> All of the callers to ib_dma_map_single(), ib_dma_map_page(),
> and ib_sg_dma_address() have been modifed to save the address
> in a u64 instead of a dma_addr_t.  This actually wasn't much
> of a change since the address was being cast to u64 anway
> when assigned to struct sge.addr.

Its fixes a bug, so it actually somehow much of a change. Without it
on arch as mentioned above, ipath_dma_map_single would return only a
u32 portion of the kvaddr and later the ulp code would place this
chopped address in sge.addr and the ipath driver would use the wrong
address.

Or.