Fast cycle counter for ARM chips with SCC - patch for review.

[Mark R V Murray]

Hi *

This patch makes the ARM6 kernels that have an SCC coprocessor (RPI and WANDBOARD have them) get a MUCH better implementation of get_cyclecount(9), but not a perfect one. The incrementing rate is good (+- 1 per instruction), but its only 32 bits. Later, if there is interest, I may wish to fix that with an overflow interrupt, but for now its easily good enough for the kernel entropy harvesting service. Also, its MUUUCH more efficient; a simple read rather can calling the internal kernel binuptime(9) clock.

Comments, please? I’m keen to commit.

M
-- 
Mark R V Murray
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