On Tue, 2010-04-27 at 16:56 -0500, Tseng-Hui (Frank) Lin wrote: > On Sat, 2010-04-24 at 10:55 +1000, Benjamin Herrenschmidt wrote: > > On Fri, 2010-04-23 at 17:04 -0500, Tseng-Hui (Frank) Lin wrote: > > > Add Power7 icswx co-processor instruction support. > > > > Please provide a -much- more detailed explanation of what it is, what it > > does and why it requires hooking into the MMU context switch code. _I_ > > know these things but nobody else on the list does which limits the > > ability of people to review your patch. > > > > icswx is a PowerPC co-processor instruction to send data to a > co-processor. On Book-S processors the LPAR_ID and process ID (PID) of > the owning process are registered in the window context of the > co-processor at initial time. When the icswx instruction is executed, > the L2 generates a cop-reg transaction on PowerBus. The transaction has > no address and the processor does not perform an MMU access to > authenticate the transaction. The coprocessor compares the LPAR_ID and > the PID included in the transaction and the LPAR_ID and PID held in the > window context to determine if the process is authorized to generate the > transaction.
How does userspace discover that there are coprocessors to send requests to? And how does the coprocessor send results back to the process? cheers
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