On Mon, 2015-01-05 at 18:46 +0100, Andreas Mohr wrote: > Hi, > > > I was curious why the mpic_cpu_read(MPIC_INFO(CPU_WHOAMI)) was there in > > the first place and if it's still needed. If it's still required, I > > guess a better approach is to eliminate the call only if the kernel is > > running on the KVM guest side, where the MPIC is emulated and no longer > > requires a readback. > > "Why not?" > > A mechanism being "emulated"/"virtual" or not > may not necessarily be much of a distinction (if at all!). > The readback might be required > to properly fulfill all requirements > of a full state change protocol specification, > which might easily be the case for both RS(*) and virtual hardware. > And especially for virtual hardware > such a "readback" event > might be an extremely important "end of transaction" marker > which may often be needed for freeing of temporary resources etc.
In that case it was purely something we added after trial and error to correct a problem, it's not specified as necessary. Basically it's about making the store synchronous to the MPIC logic. It's definitely not necessary on an emulated implementation. > I'm talking out of my *ss without any MPIC specifics here > (and especially not why the readback there actually is needed - > if that doesn't happen to be the case for PCI Posting reasons or some such), > but it's just intended as food for thought :) > > *) Real Silicon (rather than RL - Real Life) > > HTH, > > Andreas Mohr > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
