Rafael J. Wysocki had written, on 09/22/2010 07:03 PM, the following:
[Trimming the CC list slightly.]
[...]
...
First, thanks for addressing the previous comments, things look much better
now. In particular the documentation has been improved a lot in my view.
Thanks for the excellent reviews :)
[...]
+
+WARNING on OPP List Modification Vs Query operations:
+----------------------------------------------------
+The OPP layer's query functions are expected to be used in multiple contexts
+(including calls from interrupt locked context) based on SoC framework
+implementation. Only OPP modification functions are guaranteed exclusivity by
+the OPP library. Exclusivity between query functions and modification functions
+should be handled by the users such as the SoC framework appropriately; else,
+there is a risk for the query functions to retrieve stale data.
Well, this sounds like a good use case for RCU.
Kevin did point out rwlock but am I confusing with
http://lwn.net/Articles/364583/
If I get the message right, rwlock is more or less on it's way out?
[...]
+static struct device_opp *find_device_opp(struct device *dev)
+{
+ struct device_opp *tmp_dev_opp, *dev_opp = ERR_PTR(-ENODEV);
+
+ if (unlikely(!dev || IS_ERR(dev))) {
+ pr_err("%s: Invalid parameters being passed\n", __func__);
+ return ERR_PTR(-EINVAL);
+ }
+
+ list_for_each_entry(tmp_dev_opp, &dev_opp_list, node) {
+ if (tmp_dev_opp->dev == dev) {
+ dev_opp = tmp_dev_opp;
+ break;
+ }
+ }
As I said, it seems you can use RCU read locking around the list traversal
to protect it from concurrent modification.
+ return dev_opp;
+}
+
[...]
+struct opp *opp_find_freq_exact(struct device *dev,
+ unsigned long freq, bool available)
+{
+ struct device_opp *dev_opp;
+ struct opp *temp_opp, *opp = ERR_PTR(-ENODEV);
+
+ dev_opp = find_device_opp(dev);
+ if (IS_ERR(dev_opp))
+ return opp;
+
+ list_for_each_entry(temp_opp, &dev_opp->opp_list, node) {
+ if (temp_opp->available == available &&
+ temp_opp->rate == freq) {
+ opp = temp_opp;
+ break;
+ }
+ }
+
Same here.
+ return opp;
+}
+
+/**
+ * opp_find_freq_ceil() - Search for an rounded ceil freq
+ * @dev: device for which we do this operation
+ * @freq: Start frequency
+ *
+ * Search for the matching ceil *available* OPP from a starting freq
+ * for a device.
+ *
+ * Returns matching *opp and refreshes *freq accordingly, else returns
+ * ERR_PTR in case of error and should be handled using IS_ERR.
+ *
+ * Example usages:
+ * * find match/next highest available frequency *
+ * freq = 350000;
+ * opp = opp_find_freq_ceil(dev, &freq))
+ * if (IS_ERR(opp))
+ * pr_err("unable to find a higher frequency\n");
+ * else
+ * pr_info("match freq = %ld\n", freq);
+ *
+ * * print all supported frequencies in ascending order *
+ * freq = 0; * Search for the lowest available frequency *
+ * while (!IS_ERR(opp = opp_find_freq_ceil(OPP_MPU, &freq)) {
+ * pr_info("freq = %ld\n", freq);
+ * freq++; * for next higher match *
+ * }
I think it's sufficient to put the examples into the doc (the ones below too).
Ack. thanks for pointing it out.. will fix in v4.
+ freq_table[i].index = i;
+ freq_table[i].frequency = CPUFREQ_TABLE_END;
+
+ *table = &freq_table[0];
+}
+#endif /* CONFIG_CPU_FREQ */
The rest looks fine to me.
thx.
--
Regards,
Nishanth Menon
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