PM / OPP: Update Documentation to remove RCU specific bits
Update OPP documentation to remove the RCU specific bits.
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/Documentation/power/opp.txt b/Documentation/power/opp.txt
index c6279c2..0c007e2 100644
--- a/Documentation/power/opp.txt
+++ b/Documentation/power/opp.txt
@@ -79,22 +79,6 @@
specific framework which uses the OPP library. Similar care needs to be taken
care to refresh the cpufreq table in cases of these operations.
-WARNING on OPP List locking mechanism:
--------------------------------------------------
-OPP library uses RCU for exclusivity. RCU allows the query functions to operate
-in multiple contexts and this synchronization mechanism is optimal for a read
-intensive operations on data structure as the OPP library caters to.
-
-To ensure that the data retrieved are sane, the users such as SoC framework
-should ensure that the section of code operating on OPP queries are locked
-using RCU read locks. The opp_find_freq_{exact,ceil,floor},
-opp_get_{voltage, freq, opp_count} fall into this category.
-
-opp_{add,enable,disable} are updaters which use mutex and implement it's own
-RCU locking mechanisms. These functions should *NOT* be called under RCU locks
-and other contexts that prevent blocking functions in RCU or mutex operations
-from working.
-
2. Initial OPP List Registration
================================
The SoC implementation calls dev_pm_opp_add function iteratively to add OPPs per
@@ -137,15 +121,18 @@
found, else returns error. These errors are expected to be handled by standard
error checks such as IS_ERR() and appropriate actions taken by the caller.
+Callers of these functions shall call dev_pm_opp_put() after they have used the
+OPP. Otherwise the memory for the OPP will never get freed and result in
+memleak.
+
dev_pm_opp_find_freq_exact - Search for an OPP based on an *exact* frequency and
availability. This function is especially useful to enable an OPP which
is not available by default.
Example: In a case when SoC framework detects a situation where a
higher frequency could be made available, it can use this function to
find the OPP prior to call the dev_pm_opp_enable to actually make it available.
- rcu_read_lock();
opp = dev_pm_opp_find_freq_exact(dev, 1000000000, false);
- rcu_read_unlock();
+ dev_pm_opp_put(opp);
/* dont operate on the pointer.. just do a sanity check.. */
if (IS_ERR(opp)) {
pr_err("frequency not disabled!\n");
@@ -163,9 +150,8 @@
frequency.
Example: To find the highest opp for a device:
freq = ULONG_MAX;
- rcu_read_lock();
- dev_pm_opp_find_freq_floor(dev, &freq);
- rcu_read_unlock();
+ opp = dev_pm_opp_find_freq_floor(dev, &freq);
+ dev_pm_opp_put(opp);
dev_pm_opp_find_freq_ceil - Search for an available OPP which is *at least* the
provided frequency. This function is useful while searching for a
@@ -173,17 +159,15 @@
frequency.
Example 1: To find the lowest opp for a device:
freq = 0;
- rcu_read_lock();
- dev_pm_opp_find_freq_ceil(dev, &freq);
- rcu_read_unlock();
+ opp = dev_pm_opp_find_freq_ceil(dev, &freq);
+ dev_pm_opp_put(opp);
Example 2: A simplified implementation of a SoC cpufreq_driver->target:
soc_cpufreq_target(..)
{
/* Do stuff like policy checks etc. */
/* Find the best frequency match for the req */
- rcu_read_lock();
opp = dev_pm_opp_find_freq_ceil(dev, &freq);
- rcu_read_unlock();
+ dev_pm_opp_put(opp);
if (!IS_ERR(opp))
soc_switch_to_freq_voltage(freq);
else
@@ -208,9 +192,8 @@
implementation might choose to do something as follows:
if (cur_temp < temp_low_thresh) {
/* Enable 1GHz if it was disabled */
- rcu_read_lock();
opp = dev_pm_opp_find_freq_exact(dev, 1000000000, false);
- rcu_read_unlock();
+ dev_pm_opp_put(opp);
/* just error check */
if (!IS_ERR(opp))
ret = dev_pm_opp_enable(dev, 1000000000);
@@ -224,9 +207,8 @@
choose to do something as follows:
if (cur_temp > temp_high_thresh) {
/* Disable 1GHz if it was enabled */
- rcu_read_lock();
opp = dev_pm_opp_find_freq_exact(dev, 1000000000, true);
- rcu_read_unlock();
+ dev_pm_opp_put(opp);
/* just error check */
if (!IS_ERR(opp))
ret = dev_pm_opp_disable(dev, 1000000000);
@@ -249,10 +231,9 @@
soc_switch_to_freq_voltage(freq)
{
/* do things */
- rcu_read_lock();
opp = dev_pm_opp_find_freq_ceil(dev, &freq);
v = dev_pm_opp_get_voltage(opp);
- rcu_read_unlock();
+ dev_pm_opp_put(opp);
if (v)
regulator_set_voltage(.., v);
/* do other things */
@@ -266,12 +247,12 @@
{
/* do things.. */
max_freq = ULONG_MAX;
- rcu_read_lock();
max_opp = dev_pm_opp_find_freq_floor(dev,&max_freq);
requested_opp = dev_pm_opp_find_freq_ceil(dev,&freq);
if (!IS_ERR(max_opp) && !IS_ERR(requested_opp))
r = soc_test_validity(max_opp, requested_opp);
- rcu_read_unlock();
+ dev_pm_opp_put(max_opp);
+ dev_pm_opp_put(requested_opp);
/* do other things */
}
soc_test_validity(..)
@@ -289,7 +270,6 @@
soc_notify_coproc_available_frequencies()
{
/* Do things */
- rcu_read_lock();
num_available = dev_pm_opp_get_opp_count(dev);
speeds = kzalloc(sizeof(u32) * num_available, GFP_KERNEL);
/* populate the table in increasing order */
@@ -298,8 +278,8 @@
speeds[i] = freq;
freq++;
i++;
+ dev_pm_opp_put(opp);
}
- rcu_read_unlock();
soc_notify_coproc(AVAILABLE_FREQs, speeds, num_available);
/* Do other things */