On 01/14/2010 03:05 PM, Alan Cox wrote:
We need to use the MMIO BAR at least for starting DMA transfers, the
I/O ones are 64KB-limited. We can't just use read[bw] if reading all
32 bits has side effects.
Last time I instrumented this on x86 we never issued a> 64K linear block
in our s/g lists. In fact we went for years before anyone noticed we had
a bug with CS5530 and a couple of other chips that mishandled 64K segment
sizes, and that was only finally noticed in a very specific and weird
circumstance.
Having a block over 64KB may be rare, but the other thing that the large
block transfer feature does is remove the restriction on a block
crossing a 64KB boundary, which based on the experiments I did when I
worked on adding the feature, does happen fairly commonly if the driver
allows it.
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