Timur Tabi wrote: > Wood Scott-B07421 wrote: > > To be totally safe, we probably want to do a readback plus twi (to turn > > a data dependency into a flow dependency) before the isync. > > twi == trap word immediate?
Yes. > If so, I don't see how that will turn a data dependency into a flow > dependency. > Is that some sort of side effect of twi? It decides based on the input register (data dependency) whether to cause a trap (flow dependency). We never want it to actually trap, so we set a condition that says never trap, but the dependency is still there -- the hardware doesn't decode it as a no-op. See arch/powerpc/include/asm/io.h, it's used in the I/O read accessors. -Scott
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