Messages in this thread | | | Date | Tue, 07 Aug 2007 00:22:29 +0200 | From | Stefan Richter <> | Subject | Re: [PATCH 2.6.22.y] ieee1394: revert "sbp2: enforce 32bit DMA mapping" |
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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/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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