USB patch for better bus_dma and detachment support

[Rob]

Ian Dowse wrote:
> In case anybody is interested in testing or helping with this,
> there's a patch at
> 
> 	http://people.freebsd.org/~iedowse/usb.diff
> 
> that attempts to begin addressing a number of problems with our
> current USB code:
> 
>  o All data buffers were allocated using bus_dma as physically
>    contiguous memory. All transfers involve a memory copy to/from
>    these contiguous buffers, and the contiguous memory is never
>    freed. Use of these buffers is also inefficient, so low-memory
>    systems tend to quickly run out of usable physical memory.
> 
>  o USB host controllers cannot be detached, so for example, unplugging
>    a cardbus USB device will cause a crash.
> 
> Neither of these issues is completely solved by the patch, but most
> I/O now avoids the need for contiguous buffers by using bus_dmamap_load()
> on the virtual buffer, and the system seems to survive the removal
> of a cardbus OHCI/EHCI controller, though memory is probably leaked.

Can I apply this patch safely to STABLE as well?
If not, then, if you make a patch for STABLE, I would test it right away!

My umass storage USB toy, crashes the system when I umount it.
I blamed the USB chipset (VIA 83C572 USB controller), but am still not sure,
since I did not get much response from the STABLE mailing list.

It would be great if your patch would solve the crash!

Regards,
Rob.