On Saturday 08 November 2008, Hans Petter Selasky wrote:
> On Saturday 08 November 2008, Alexander Motin wrote:


> What is the real reason to do that? If you are saying that you uses
> 1-byte alignment then you should be able to accept _any_ address that
> busdma will allocate to you! Why original data alignment should so
> strictly affect hardware operation?


Hi,

The real reason is that the EHCI and OHCI only takes the full physical address
of the _first_ page, and then for the subsequent pages only stores the upper
bits of the physical address, leaving it impossible to program a per-page
data start offset. The hardware assumes that the lower part of the physical
address wraps modulo PAGE_SIZE, and that's it. Don't ask me why they designed
it like that. Currently USB is broken on all architectures where bouncing is
used. I see no other way around this than to change busdma.

--HPS
_______________________________________________
freebsd-current@freebsd.org mailing list
http://lists.freebsd.org/mailman/lis...reebsd-current
To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org"