On 11/24/21 7:58 PM, William Breathitt Gray wrote:
On Wed, Nov 24, 2021 at 08:27:20AM +0100, Oleksij Rempel wrote:
Hi William,
On Wed, Nov 24, 2021 at 03:09:05PM +0900, William Breathitt Gray wrote:
On Tue, Nov 23, 2021 at 02:45:40PM +0100, Oleksij Rempel wrote:
Add counter_push_event() to notify user space about new pulses
Signed-off-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
---
drivers/counter/interrupt-cnt.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/counter/interrupt-cnt.c b/drivers/counter/interrupt-cnt.c
index 8514a87fcbee..b237137b552b 100644
--- a/drivers/counter/interrupt-cnt.c
+++ b/drivers/counter/interrupt-cnt.c
@@ -31,6 +31,8 @@ static irqreturn_t interrupt_cnt_isr(int irq, void *dev_id)
atomic_inc(&priv->count);
+ counter_push_event(&priv->counter, COUNTER_EVENT_OVERFLOW, 0);
+
return IRQ_HANDLED;
}
--
2.30.2
Hi Oleksij,
It looks like this is pushing a COUNTER_EVENT_OVERFLOW event every time
an interrupt is handled, which I suspect is not what you want to happen.
The COUNTER_EVENT_OVERFLOW event indicates a count value overflow event,
so you'll need to check for a count value overflow before pushing the
event.
It would be good idea to implement a ceiling extension as well (you can
use the COUNTER_COMP_CEILING() macro) so that users can configure the
particular point where the value overflows.
Thank you!
What would be the best and resource effective strategy for periodically
getting frequency of interrupts/pulses? This is actual information which is
needed for my use case.
So far, I was pushing every event to the user space, which is working
but probably not the most resource effective method of doing it.
Regards,
Oleskij
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We could introduce a new Counter change-of-state event type which would
trigger whenever the count value changes, but I agree with you that this
is likely not the best way for us to derive the frequency of the
interrupts due to the indirection of handling and parsing the event
data.
Instead, perhaps introducing a "frequency" or "period" Count extension
would make more sense here. This extension could report the value delta
between counts, or alternatively the time delta from which you can
derive frequency. Regarding implementation, you can store the previous
value in a variable, updating it whenever an interrupt occurs, and
compute the particular delta every time a read is requested by the user.
David Lechner is implementing something similar for the TI eQEP driver
to expose speed, so I'm CCing them here in case this is of interest to
them.
Based on my experience, I would recommend that counter drivers be as
"thin" as possible. They shouldn't try to provide any information that
the hardware itself doesn't provide. In other words, the kernel should
provide userspace the information needed to calculate the speed/rate
but not try to do the actual calculation in the kernel. Inevitably
there are nuances for specific use cases that can't all possibly be
handled by such an implementation.
I've tried using gpio interrupts to try to calculate speed/rate in
the kernel before and it simply doesn't work reliably. Interrupts
get missed and the calculation will be off.
For really slow counts (i.e. 1 count/second), I can see a use for
generating an event on each count though. For high rates, I would
just read the count every 100ms in usespace and divide the change in
the number of counts by the time period to get the rate.
