On 9/26/20 9:18 PM, William Breathitt Gray wrote:
diff --git a/drivers/counter/counter-chrdev.c b/drivers/counter/counter-chrdev.c
new file mode 100644
index 000000000000..2be3846e4105
--- /dev/null
+++ b/drivers/counter/counter-chrdev.c
+/**
+ * counter_push_event - queue event for userspace reading
+ * @counter: pointer to Counter structure
+ * @event: triggered event
+ * @channel: event channel
+ *
+ * Note: If no one is watching for the respective event, it is silently
+ * discarded.
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure.
+ */
+int counter_push_event(struct counter_device *const counter, const u8 event,
+ const u8 channel)
+{
+ struct counter_event ev = {0};
+ unsigned int copied = 0;
+ unsigned long flags;
+ struct counter_event_node *event_node;
+ struct counter_comp_node *comp_node;
+ int err;
+
+ ev.timestamp = ktime_get_ns();
+ ev.watch.event = event;
+ ev.watch.channel = channel;
+
+ raw_spin_lock_irqsave(&counter->events_lock, flags);
+
+ /* Search for event in the list */
+ list_for_each_entry(event_node, &counter->events_list, l)
+ if (event_node->event == event &&
+ event_node->channel == channel)
+ break;
+
+ /* If event is not in the list */
+ if (&event_node->l == &counter->events_list)
+ goto exit_early;
+
+ /* Read and queue relevant comp for userspace */
+ list_for_each_entry(comp_node, &event_node->comp_list, l) {
+ err = counter_get_data(counter, comp_node, &ev.value_u8);
Currently all counter devices are memory mapped devices so calling
counter_get_data() here with interrupts disabled is probably OK, but
if any counter drivers are added that use I2C/SPI/etc. that will take
a long time to read, it would cause problems leaving interrupts
disabled here.
Brainstorming: Would it make sense to separate the event from the
component value being read? As I mentioned in one of my previous
reviews, I think there are some cases where we would just want to
know when an event happened and not read any additional data anyway.
In the case of a slow communication bus, this would also let us
queue the event in the kfifo and notify poll right away and then
defer the reads in a workqueue for later.
+ if (err)
+ goto err_counter_get_data;
+
+ ev.watch.component = comp_node->component;
+
+ copied += kfifo_put(&counter->events, ev);
+ }
+
+ if (copied)
+ wake_up_poll(&counter->events_wait, EPOLLIN);
+
+exit_early:
+ raw_spin_unlock_irqrestore(&counter->events_lock, flags);
+
+ return 0;
+
+err_counter_get_data:
+ raw_spin_unlock_irqrestore(&counter->events_lock, flags);
+ return err;
+}
