Re: USB umass hard drive "failed to create xfers" when attaching

[Greg Troxel <gdt%lexort.com@localhost>]

mlelstv%serpens.de@localhost (Michael van Elst) writes:

> gdt%lexort.com@localhost (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.