[SeaBIOS] ohci bulk?

Stefan Berger stefanb at linux.vnet.ibm.com
Sat Nov 20 19:18:18 CET 2010

On 11/20/2010 01:05 PM, Kevin O'Connor wrote:
> On Sat, Nov 20, 2010 at 12:58:56PM -0500, Stefan Berger wrote:
>> On 11/20/2010 12:50 PM, Kevin O'Connor wrote:
>>> I suppose one could implement a simple SMM gateway - write a magic IO
>>> bit to invoke the SMM handler, have the SMM handler backup the cpu
>>> state somewhere in BIOS owned memory, and then leave SMM mode with
>>> execution at a BIOS handler running in 32bit flat mode.  The BIOS
>>> handler could then do its work and manually return the CPU to its
>>> initial state before returning to the guest.  The BIOS would need to
>>> ensure that it didn't allow interrupts (or NMIs) while in this mode,
>>> but that's possible.  One would probably want to ensure that the BIOS
>>> didn't touch any non-BIOS owned memory in this state as well, but
>>> that's also possible.
>> FWIW, I am currently working on a gateway for calling 32 bit
>> functions in the relocated 32bit code from 16 bit code, opening up
>> that are for more than the init functions. It works fine from what I
>> can see also considering the mixture of register and stack passing
>> of arguments. Would that be helpful here?
> Is it something like stacks.c:call32() or is it via SMM?
The way it works is that there is a jumptable with entries to the 
function in the 'high bios'. That jumptable along with all the other 32 
bit code gets relocated to upper memory and in the 'lower BIOS' I keep a 
pointer to the jumptable in the 'high bios' for the upcall code to see. 
It's basically similar to what I have previously contributed to Bochs 
BIOS in Xen, just that the upcall code can deal with parameter passed 
via registers or a limited number on the stack.


> BTW, are you reserving the relocated code or are you only doing this
> during the init phase?
The 'high bios' functions should be accessible all the time basically. 
So, the relocated code needs to be marked as e820-reserved memory -- I 
suppose that should do the trick then?


> -Kevin

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