xtensa: SMP: rework IPI processing

Don't skip current CPU in send_ipi_message: callers of this function
take care of it and it's harmless anyway.
Don't clear IPI bits one by one, clear all that were read at once.
Check IPI register in a loop in case new IPI was posted while previous
was being handled.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/kernel/smp.c

@@ -372,7 +372,6 @@ static void send_ipi_message(const struct cpumask *callmask,
 	unsigned long mask = 0;
 
 	for_each_cpu(index, callmask)
-		if (index != smp_processor_id())
 		mask |= 1 << index;
 
 	set_er(mask, MIPISET(msg_id));
@@ -412,22 +411,31 @@ irqreturn_t ipi_interrupt(int irq, void *dev_id)
 {
 	unsigned int cpu = smp_processor_id();
 	struct ipi_data *ipi = &per_cpu(ipi_data, cpu);
+
+	for (;;) {
 		unsigned int msg;
-	unsigned i;
 
 		msg = get_er(MIPICAUSE(cpu));
-	for (i = 0; i < IPI_MAX; i++)
-		if (msg & (1 << i)) {
-			set_er(1 << i, MIPICAUSE(cpu));
-			++ipi->ipi_count[i];
+		set_er(msg, MIPICAUSE(cpu));
+
+		if (!msg)
+			break;
+
+		if (msg & (1 << IPI_CALL_FUNC)) {
+			++ipi->ipi_count[IPI_CALL_FUNC];
+			generic_smp_call_function_interrupt();
 		}
 
-	if (msg & (1 << IPI_RESCHEDULE))
+		if (msg & (1 << IPI_RESCHEDULE)) {
+			++ipi->ipi_count[IPI_RESCHEDULE];
 			scheduler_ipi();
-	if (msg & (1 << IPI_CALL_FUNC))
-		generic_smp_call_function_interrupt();
-	if (msg & (1 << IPI_CPU_STOP))
+		}
+
+		if (msg & (1 << IPI_CPU_STOP)) {
+			++ipi->ipi_count[IPI_CPU_STOP];
 			ipi_cpu_stop(cpu);
+		}
+	}
 
 	return IRQ_HANDLED;
 }