Re: [Em28xx] ehci_hcd map_single: unable to map unsafe buffer on a standard NSLU2

> I am trying to understand dmabounce, why this problem occurs, and how to 
> correct it
> I hope with the help of linux-arm people...

The dmabounce code predates the change in the ARM DMA code to
require that dma_free_coherent() have IRQs enabled, and nobody
has yet submitted patches to fix that problem.  (One approach
can be seen in the code removed from the net2280 and omap_udc
drivers by patch c67ab134ba9f83f9de86e58adfeaa14a9efa6e00 ...)

The NSLU2 has this problem because it has very weak PCI DMA ...
it can only use memory from one particular range.

That issue has been discussed repeatedly on Linux-ARM-Kernel.
Russell is pretty down on dmabounce, but I don't recall him
suggesting a usable solution to working around that PCI DMA
issue on those IXP chips.


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