Re: (FWD) Serious busdma bug in -current in relation to USB harware.

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