On Wed, 2006-12-13 at 12:30 -0800, Andrew Morton wrote:
> On Wed, 13 Dec 2006 12:11:27 -0800
> Ralph Campbell <[email protected]> wrote:
snip.
> > My preference would be to change the offending uses of dma_addr_t
> > to u64. Do you have a better solution?
>
> We should be able to use dma_addr_t for this? Is it not the case that the
> values we're dealing with here _are_ DMA addresses? I think a more complete
> description of the problem we're trying to solve here would help.
>
> I'm not sure what the problem is with sparc64 - perhaps its dma_addr_t
> really is a "cookie" and isn't a physical bus address? But you want a value
> which is really a physical bus address? Dunno.
>
> Perhaps dma64_addr_t can be used here.
The fundamental problem is that ib_get_dma_mr() returns a
pointer representing a memory region for all of physical memory
and the IB interface consumer is expected to call dma_map_single()
to get a dma_addr_t to pass to the HCA driver with the memory
region pointer.
For an HCA like Mellanox, the dma_addr_t really is a DMA address
which the hardware uses to DMA data from the chip to memory.
The ib_ipath HCA driver does not generally use DMA addresses.
The hardware does DMA the receive packet to a ring of buffers
but the receive interrupt handler then has to copy the data
from the receive buffer to the address specified by the
ib_post_recv() function. This means the driver needs a
kernel virtual address instead of the memory region + DMA address
that is passed by ib_post_recv().
The ib_dma_*() functions were added to allow the ib_ipath
driver to interpose on the dma_*() functions so that a
kernel virtual address can be returned instead of allocating
an IOMMU DMA address. Without the interposing functions,
there is no way for the ib_ipath driver to convert the IOMMU
address back into a kernel virtual address since it never
sees the original inputs used to allocate the IOMMU address.
I don't want to make ib_dma_map_single() return a dma_addr_t
cookie and use it to lookup the kernel virtual address since
this is a performance critical code path in the receive
interrupt handler and the "cookie" needs to be a byte address
which can be offset within a page.
The secondary problem is that on sparc64, dma_addr_t is a
u32 so if ib_dma_map_single() returns a void * cast to dma_addr_t,
it is truncated. We might be able to convince the sparc64
maintainers to make dma_addr_t u64 but dma64_addr_t won't
work because that is specific to sparc64. The type has
to be architecture neutral.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
