soc: intel_adsp/ace: fix IDC processing for sched IPI

The Inter-DSP Communication (IDC) is being used to send
sched IPI to other CPU cores. When a core receives an IDC,
it needs to ACK it by clearing the BUSY bit in TDR, and also
needs to the BUSY bit in TDA to signal done after processing.
These two steps are needed to complete one IDC message.
If we do only one (and not both), the other side will not be
able to send another IDC message as the hardware still thinks
the core is processing the IDC message (and thus will not send
another one). So add the step to clear the BUSY bit in TDA so
we can have multiple sched IPIs.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>

Author: dcpleung

soc/xtensa/intel_adsp/ace/multiprocessing.c

@@ -16,7 +16,20 @@
 
 static void ipc_isr(void *arg)
 {
-	IDC[arch_proc_id()].agents[0].ipc.tdr = BIT(31); /* clear BUSY bit */
+	uint32_t cpu_id = arch_proc_id();
+
+	/*
+	 * Clearing the BUSY bits in both TDR and TDA are needed to
+	 * complete an IDC message. If we do only one (and not both),
+	 * the other side will not be able to send another IDC
+	 * message as the hardware still thinks you are processing
+	 * the IDC message (and thus will not send another one).
+	 * On TDR, it is to write one to clear, while on TDA, it is
+	 * to write zero to clear.
+	 */
+	IDC[cpu_id].agents[0].ipc.tdr = BIT(31);
+	IDC[cpu_id].agents[0].ipc.tda = 0;
+
 #ifdef CONFIG_SMP
 	void z_sched_ipi(void);
 	z_sched_ipi();