Cristian Marussi a0ba2a97fd scmi: Protect SCMI/SMT channels from concurrent transmissions ... The SCMI/SMT memory areas are used from the agent and the platform as channels to exchage commands and replies. Once the platform has completed its processing and a reply is ready to be read from the agent, the platform will relinquish the channel to the agent by setting the CHANNEL_FREE bits in the related SMT area. When this happens, though, the agent has still to effectively read back the reply message and any other concurrent request happened to have been issued in the meantime will have been to be hold back until the reply is processed or risk to be overwritten by the new request. The base->mtx lock that currently guards the whole scmi_request() operation is released when sleeping waiting for a reply, so the above mentioned race can still happen or, in a slightly different scenario, the concurrent transmission could just fail, finding the channel busy, after having sneaked through the mutex. Adding a new mechanism to let the agent explicitly acquire/release the channel paves the way, in the future, to remove such central commmon lock in favour of new dedicated per-transport locking mechanisms, since not all transports will necessarily need the same level of protection. Add a flag, controlled by the agent, to mark when the channel has an inflight command transaction still pending to be completed and make the agent spin on it when queueing multiple concurrent messages on the same SMT channel. Reviewed by: andrew Tested on: Arm Morello Board Sponsored by: Arm Ltd Differential Revision: https://reviews.freebsd.org/D43043		2024-04-11 09:58:56 +00:00
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arm	scmi: Protect SCMI/SMT channels from concurrent transmissions	2024-04-11 09:58:56 +00:00
xilinx	Trim various $FreeBSD$	2023-10-10 10:34:43 -07:00