[LinuxBIOS] USB Support <WAS Re: Accessibility of LinuxBios>

Eric W. Biederman ebiederman at lnxi.com
Mon Jul 3 11:56:32 CEST 2006

Stefan Reinauer <stepan at coresystems.de> writes:

> * yhlu <yinghailu at gmail.com> [060703 03:31]:
>> 2. use cpu cache for ohci or uhci buffer for packet.
> Don't they circumvent the CPU to access the memory?

Depends on the cpu.  As I recall Intel cpus flush data to memory
for all of their cache coherence, so I don't think it would work
there.  I think AMD is some better in this regard, but I would be
surprised if it worked.  It makes sense to research it though.

So if we have to use DMA it looks like we are out of luck until
after memory is initialized.  Ouch!.

So sending some really simply usb commands out the EHCI debug port
looks really interesting.  If that works it is also very interesting
for debugging kernels on modern hardware as well.


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