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For any remote call to DSP, after sending an invocation message, the fastRPC driver waits for a glink response, during which the CPU can enter low power modes. This adds latency to the fastRPC call due to CPU wakeup and scheduling overhead. Add polling mode support where the fastRPC driver polls a shared memory location for completion after sending the invocation, avoiding CPU wakeup and scheduling latency and reducing fastRPC overhead. If the poll times out, the call falls back to the normal interrupt/glink-based completion path. Poll mode is only applied to dynamic modules running in a user PD (handle > FASTRPC_MAX_STATIC_HANDLE), since static/root-PD handles are not expected to benefit from, or require, this optimization. Support is advertised per SoC via fastrpc_soc_data, with a closed exception list for older platforms whose DSP firmware is known to support polling but which otherwise use the default soc_data. Poll mode can be enabled by userspace via the FASTRPC_IOCTL_SET_OPTION ioctl with the FASTRPC_POLL_MODE request id. Since context IDs (ctxid) are allocated from a fixed-size, per-channel cyclic IDR shared by all processes on a DSP, a context ID can be recycled for a new request soon after it is freed. In poll mode the context can be considered complete (and released) as soon as the poll memory is updated, while the corresponding glink COMPLETE response from the DSP may still be in flight. If that response arrives after the ctxid has been reused, it would otherwise match the new context and incorrectly signal completion for it while the DSP may still be operating on the new context's buffers. To prevent this, embed a monotonically increasing per-channel sequence number in the unused upper bits of the ctxid/message context and validate it in the rpmsg callback, dropping any response whose sequence number does not match the current owner of that ctxid slot. Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com> Signed-off-by: Srinivas Kandagatla <srini@kernel.org> Link: https://patch.msgid.link/20260729094352.111065-8-srini@kernel.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>