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Is this >> not sufficient? >> > Yes, it is not enough. > Once send_data() return success, platform can receive an interrupt，but > the processing of the platform has not ended. > This processing includes handling data and then triggering an > interrupt to notify OS. This comment caused me to rethink how I was using the PCC mailbox API.  I realized that it was not actually enforcing the PCC protocol, which you identified.  It lead me to rewrite a postion of the PCC Mailbox API, and that is in my next patch series.  I would appreciate it if you would take a look. I think it addresses this concern, but it might not be completely transparent to a reviewer.   I would greatly appreciate if you were to look at it and confirm it fixes the issue, or, if I have missed something, let me know what you see.