PM: QoS: Add check to make sure CPU latency is non-negative

CPU latency should never be negative, which will be incorrectly high
when converted to unsigned data type.

Commit 8d36694 ("PM: QoS: Add check to make sure CPU freq is
non-negative") makes sure CPU frequency is non-negative to fix incorrect
behavior in freqency QoS.

Add an analogous check to make sure CPU latency is non-negative so as to
prevent this problem from happening in CPU latency QoS.

Signed-off-by: Clive Lin <clive.lin@mediatek.com>
[ rjw: Changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: Clive Lin

kernel/power/qos.c

@@ -220,6 +220,11 @@ static struct pm_qos_constraints cpu_latency_constraints = {
 	.type = PM_QOS_MIN,
 };
 
+static inline bool cpu_latency_qos_value_invalid(s32 value)
+{
+	return value < 0 && value != PM_QOS_DEFAULT_VALUE;
+}
+
 /**
  * cpu_latency_qos_limit - Return current system-wide CPU latency QoS limit.
  */
@@ -263,7 +268,7 @@ static void cpu_latency_qos_apply(struct pm_qos_request *req,
  */
 void cpu_latency_qos_add_request(struct pm_qos_request *req, s32 value)
 {
-	if (!req)
+	if (!req || cpu_latency_qos_value_invalid(value))
 		return;
 
 	if (cpu_latency_qos_request_active(req)) {
@@ -289,7 +294,7 @@ EXPORT_SYMBOL_GPL(cpu_latency_qos_add_request);
  */
 void cpu_latency_qos_update_request(struct pm_qos_request *req, s32 new_value)
 {
-	if (!req)
+	if (!req || cpu_latency_qos_value_invalid(new_value))
 		return;
 
 	if (!cpu_latency_qos_request_active(req)) {