[coreboot] libpayload TSC dependency

bifferos bifferos at yahoo.co.uk
Wed Jan 13 14:14:52 CET 2010

I've hacked up a version of libpayload which doesn't depend on TSC 
to get payloads running on my platform.  It seems an unnecessary limitation of the library that it needs this, and also that it 
checks CPU speed before the payload main() is called, meaning 
you can't avoid it in your payload implementation without 
recompilation of the lib.

I was just wondering if there would be any interest in a patch 
to remove the dependency.  It doesn't look too tricky, however 
the ndelay function is hard to implement without TSC.  Is this 
function really needed?  Which payloads are likely to suffer
if it's inaccurate?  mdelay can be pretty accurate using the 
PIT, udelay could perhaps be based on port 80 reads instead.

A scheme could be put in place to detect the TSC instruction 
and fall back on alternative routines if it doesn't exist, 
however as far as I can see this will involve creation of 
an illegal instruction trap, setting up the IDT etc, which 
might not be desirable.  Removing TSC altogether may be 
more appropriate, especially if the ndelay() routine isn't 
really needed (my CPU is 150MHz).

Or we could just add a compilation option, however since 
libpayload is a library I don't think that's ideal.

Any thoughts?

kind regards,


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