Messages in this thread | | | Date | Mon, 5 Jan 2015 18:46:16 +0100 | From | Andreas Mohr <> | Subject | Re: [RFC] PPC: MPIC: necessary readback after EOI? |
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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.
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
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