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SubjectRe: [PATCH 2.6.22.y] ieee1394: revert "sbp2: enforce 32bit DMA mapping"
Benjamin Herrenschmidt wrote:
> Oh and, don't do the set_dma_mask() in sbp2, it has nothing to do there.
> It should be in the ohci1394 driver.

That's not quite right. OHCI-1394 implementations can go beyond 4GB bus
address space. (Although I don't know if there are such implementations
available. At least there are two implementations which can set the
so-called Physical Range bigger than 4GB.)

Sbp2 however requires that everything which it DMA-maps resides in the
Physical Range of the controller. This way the CPU is not involved in
most of the data transfers. The OHCI-1394 controller acts as bus bridge
between IEEE 1394 bus and local bus, with a 1:1 mapping of IEEE 1394 bus
addresses to and from local bus addresses --- but not in the whole 48
bits white IEEE 1394 bus address range, only in the
implementation-dependent Physical Range. The minimum Physical Range
that all OHCI-1394 implementations guarantee is 4GB. I could actually
have set a bigger mask in sbp2 when the controller supports a
programmable bigger range.

So that's the story why that dma_set_mask went into sbp2: Sbp2 wants
mappings in a _subset_ of the OHCI-1394 controllers DMA range.

Anyway. For now I will simply go with what 2.6.23-rc has and what
2.6.21 had: No dma_set_mask anywhere in the 1394 subsystem. We can
revisit this whenever an actual need arises.
--
Stefan Richter
-=====-=-=== =--- --==-
http://arcgraph.de/sr/
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