consistent_dma_mask is a ghost?
From: Krzysztof Halasa
Date: Mon Aug 11 2003 - 18:12:59 EST
[Repost, not sure why it haven't reach the list]
Hi,
I've run grep over the linux-2.6.0-test3 tree and it seems the whole
"consistent_dma_mask" thing does not really exist.
The following files reference it, either as a variable struct pci_dev*
dev->consistent_dma_mask or function set_consistent_dma_mask():
drivers/net/tg3.c: sets both consistent_dma_mask and dma_mask to 2^64-1,
and if that fails to 2^32-1.
drivers/atm/lanai.c: sets both to 2^32-1 = the default
drivers/pci/pci.c: the function pci_set_consistent_dma_mask() itself
drivers/pci/probe.c: sets default 2^32-1 for a device;
arch/ia64/sn/io/machvec/pci_dma.c: sn_pci_alloc_consistent() actually uses
consistent_dma_mask
arch/x86_64/kernel/pci-gart.c: pci_alloc_consistent() actually uses
consistent_dma_mask
This means that only _two_ platforms, ia64 and x86_64, have means to use
that information, and other platforms use set_dma_mask() and dev->dma_mask
for consistent (coherent) allocations ignoring consistent_dma_mask at all
(and possibly allocating memory from invalid region, if the masks are
not equal).
No wonder even on those two platforms no code uses consistent_dma_mask
to do some real work - i.e. both tg3 and lanai drivers use the same value
for consistent and streaming mapping. The "DMA" API doesn't have anything
like this either.
Is the whole thing a work in progress, only partially merged, and will we
see this working as documented, or should we just remove all traces of
useless consistent_dma_mask and use a single dma_mask for both kinds of
mapping? Should I prepare the patch?
Another problem, common to DMA API and PCI API:
Unless I'm mistaken, both dma_map_* and pci_map_* claim to use dma_mask
to return dma_addr_t bus address for a device. At least on i386, there
is no such thing at all - the returned address is just a result of
virt_to_phys(), and is not limited by the mask. I understand doing that
in accordance to the docs would sometimes mean memcpy() (with devices
using smaller than 2^32-1 dma_mask). Should the code be corrected/added
or are the docs to be changed to reflect reality?
--
Krzysztof Halasa
Network Administrator
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/