OPP: Level zero is valid

The level zero can be used by some OPPs to drop performance state vote
for the device. It is perfectly fine to allow the same.

_set_opp_level() considers it as an invalid value currently and returns
early.

In order to support this properly, initialize the level field with
U32_MAX, which denotes unused level field.

Reported-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Author: vireshk

drivers/opp/core.c

@@ -201,7 +201,7 @@ EXPORT_SYMBOL_GPL(dev_pm_opp_get_freq_indexed);
  * @opp:	opp for which level value has to be returned for
  *
  * Return: level read from device tree corresponding to the opp, else
- * return 0.
+ * return U32_MAX.
  */
 unsigned int dev_pm_opp_get_level(struct dev_pm_opp *opp)
 {
@@ -221,7 +221,7 @@ EXPORT_SYMBOL_GPL(dev_pm_opp_get_level);
  * @index:	index of the required opp
  *
  * Return: performance state read from device tree corresponding to the
- * required opp, else return 0.
+ * required opp, else return U32_MAX.
  */
 unsigned int dev_pm_opp_get_required_pstate(struct dev_pm_opp *opp,
 					    unsigned int index)
@@ -808,6 +808,14 @@ struct dev_pm_opp *dev_pm_opp_find_level_ceil(struct device *dev,
 	struct dev_pm_opp *opp;
 
 	opp = _find_key_ceil(dev, &temp, 0, true, _read_level, NULL);
+
+	/* False match */
+	if (temp == OPP_LEVEL_UNSET) {
+		dev_err(dev, "%s: OPP levels aren't available\n", __func__);
+		dev_pm_opp_put(opp);
+		return ERR_PTR(-ENODEV);
+	}
+
 	*level = temp;
 	return opp;
 }
@@ -1049,12 +1057,18 @@ static int _set_opp_bw(const struct opp_table *opp_table,
 static int _set_performance_state(struct device *dev, struct device *pd_dev,
 				  struct dev_pm_opp *opp, int i)
 {
-	unsigned int pstate = likely(opp) ? opp->required_opps[i]->level: 0;
+	unsigned int pstate = 0;
 	int ret;
 
 	if (!pd_dev)
 		return 0;
 
+	if (likely(opp)) {
+		pstate = opp->required_opps[i]->level;
+		if (pstate == OPP_LEVEL_UNSET)
+			return 0;
+	}
+
 	ret = dev_pm_domain_set_performance_state(pd_dev, pstate);
 	if (ret) {
 		dev_err(dev, "Failed to set performance state of %s: %d (%d)\n",
@@ -1135,7 +1149,7 @@ static int _set_opp_level(struct device *dev, struct opp_table *opp_table,
 	int ret = 0;
 
 	if (opp) {
-		if (!opp->level)
+		if (opp->level == OPP_LEVEL_UNSET)
 			return 0;
 
 		level = opp->level;
@@ -1867,6 +1881,8 @@ struct dev_pm_opp *_opp_allocate(struct opp_table *opp_table)
 
 	INIT_LIST_HEAD(&opp->node);
 
+	opp->level = OPP_LEVEL_UNSET;
+
 	return opp;
 }
 

drivers/opp/of.c

@@ -1393,8 +1393,14 @@ int of_get_required_opp_performance_state(struct device_node *np, int index)
 
 	opp = _find_opp_of_np(opp_table, required_np);
 	if (opp) {
-		pstate = opp->level;
+		if (opp->level == OPP_LEVEL_UNSET) {
+			pr_err("%s: OPP levels aren't available for %pOF\n",
+			       __func__, np);
+		} else {
+			pstate = opp->level;
+		}
 		dev_pm_opp_put(opp);
+
 	}
 
 	dev_pm_opp_put_opp_table(opp_table);

include/linux/pm_opp.h

@@ -92,9 +92,12 @@ struct dev_pm_opp_config {
 	struct device ***virt_devs;
 };
 
+#define OPP_LEVEL_UNSET			U32_MAX
+
 /**
  * struct dev_pm_opp_data - The data to use to initialize an OPP.
- * @level: The performance level for the OPP.
+ * @level: The performance level for the OPP. Set level to OPP_LEVEL_UNSET if
+ * level field isn't used.
  * @freq: The clock rate in Hz for the OPP.
  * @u_volt: The voltage in uV for the OPP.
  */