I've looked, and it doesn't appear that the kernel uses any mac
instructions, nor does it read the MAC sprs using mfspr. (Which is
surprising as I would expect the kernel to save them during context
switches.)
This is a known deficiency...
eCos does the opposite, it always saves and restores the MAC SPRs, and
that triggers a trap in my CPU implementation, which has no MAC unit yet.
Should you decide to fix this issue in Linux, I would suggest that you
either check at runtime whether the MAC unit is implemented (there is a
"unit presence" register in the spec), or that you provide a Linux
kernel config setting.
Thanks,
rdiez
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