IPCMxSEND
writel_relaxed(2, ipc_base + IPCMxSEND(IPC_RX_MBOX));
writel_relaxed(0, ipc_base + IPCMxSEND(IPC_TX_MBOX));
writel_relaxed(0x1, ipc_base + IPCMxSEND(mbox));
writel_relaxed(0, ipc_base + IPCMxSEND(IPC_TX_MBOX));