Re: [PATCH 04/17] PM / OPP: Introduce dev_pm_opp_get_max_volt_latency()
From: Stephen Boyd <hidden>
Date: 2016-01-12 19:45:39
On 01/12, Viresh Kumar wrote:
quoted hunk ↗ jump to hunk
diff --git a/drivers/base/power/opp/core.c b/drivers/base/power/opp/core.c index 052fc6b78dc3..62976d0bd61c 100644 --- a/drivers/base/power/opp/core.c +++ b/drivers/base/power/opp/core.c@@ -231,8 +231,62 @@ unsigned long dev_pm_opp_get_max_clock_latency(struct device *dev) EXPORT_SYMBOL_GPL(dev_pm_opp_get_max_clock_latency); /** + * dev_pm_opp_get_max_volt_latency() - Get max voltage latency in nanoseconds + * @dev: device for which we do this operation + * + * Return: This function returns the max voltage latency in nanoseconds. + * + * Locking: This function takes rcu_read_lock().
False.
+ */
+unsigned long dev_pm_opp_get_max_volt_latency(struct device *dev)
+{
+ struct device_opp *dev_opp;
+ struct dev_pm_opp *opp;
+ struct regulator *reg;
+ unsigned long latency_ns = 0;
+ unsigned long min_uV = ~0, max_uV = 0;
+ int ret;
+
+ /*
+ * Hold our list modification lock here as regulator_set_voltage_time()
+ * can possibly take another mutex, which isn't allowed within rcu
+ * locks.
+ */
+ mutex_lock(&dev_opp_list_lock);So now we take the list modification mutex. Why can't we rcu_read_lock(), find the min and max voltage, and then release the read lock and ask regulator framework for the voltage time?
From what I can tell we're just trying to make sure that the list
is stable when iterating through it to find the min/max voltage.
+
+ dev_opp = _find_device_opp(dev);
+ if (IS_ERR(dev_opp))
+ goto unlock;
+
+ reg = dev_opp->regulator;
+ /* Regulator may not be available for device */
+ if (IS_ERR(reg))
+ goto unlock;
+
+ list_for_each_entry_rcu(opp, &dev_opp->opp_list, node) {
+ if (!opp->available)
+ continue;
+
+ if (opp->u_volt_min < min_uV)
+ min_uV = opp->u_volt_min;
+ if (opp->u_volt_max > max_uV)
+ max_uV = opp->u_volt_max;
+ }
+
+ ret = regulator_set_voltage_time(reg, min_uV, max_uV);
+ if (ret > 0)
+ latency_ns = ret * 1000;
+
+unlock:
+ mutex_unlock(&dev_opp_list_lock);
+
+ return latency_ns;
+}
+EXPORT_SYMBOL_GPL(dev_pm_opp_get_max_volt_latency);-- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project