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Re: USB umass hard drive "failed to create xfers" when attaching (Michael van Elst) writes:

> (Greg Troxel) writes:
>>My impression is that something, perhaps more umass than *hci, needs a
>>very large chunk of memory.
> umass allocates two 64k (MAXPHYS sized) DMA buffers and a few smaller ones.
> For all drivers but ehci each buffer must use contigous physical pages.
> ehci learned to use multiple DMA segments some time ago, so the
> error is now rare. xhci still has to learn it, other drivers may
> not be able to support it due to hardware limitations.
>>My fuzzy impression is that the standard wisdom is that drivers should
>>not demand really large continuous chunks.
> 64kbyte is not really large.

Thanks for the clarity, and agreed that 64 kB is nowhere near large.

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