Messages in this thread | | | Subject | Re: [PATCH v5 3/5] counter: Add character device interface | From | David Lechner <> | Date | Wed, 14 Oct 2020 12:43:08 -0500 |
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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; > +}
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