On 2/17/23 13:43, Jonathan Cameron wrote:
On Fri, 17 Feb 2023 07:56:22 +0200
Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
Hi Mehdi,
On 2/16/23 22:22, Mehdi Djait wrote: >>> And here are the relevant steps after an IRQ occurs :
1. IRQ context --> kx022a_irq_handler() --> gets the current timestamp
with "data->timestamp = iio_get_time_ns(idev);" and returns
IRQ_WAKE_THREAD
2. kx022a_irq_thread_handler() -> checks that the trigger is enabled
--> iio_trigger_poll_chained() --> handle_nested_irq(): which will only
call the bottom half of the pollfuncs
I don't get the kx022a at my hands until next week to test this, but it
seems to me your reasoning is right. iio_pollfunc_store_time() is
probably not called. I just wonder why I didn't see zero timestamps when
testing this. (OTOH, I had somewhat peculiar IRQ handling at first -
maybe I broke this along the way).
This is a common problem. So far we've always solved it in the driver
by using the pf->timestamp only if it's been set - otherwise fallback
to grabbing a new one to pass into iio_push_to_buffer_with_timestamp()
in the threaded handler.
It might be possible to solve in a generic fashion but it's a bit
fiddly so I don't think anyone has ever looked at it.
I agree it's "fiddly" :) I played with a though of conditionally adding
the timestamp in the iio_trigger_poll_chained() if the timestamp is zero
there. This, however, would require clearing the timestamp when it is
read - which gets "fiddly" soon. Hence I just suggested adding a note in
kerneldoc.
Question 2: If the change proposed in question 1 is wrong, would this
one be better iio_push_to_buffers_with_timestamp(idev, data->buffer,
iio_get_time_ns(idev)). There is some delay between the IRQ occuring
and trigger_handler being called but that is better than getting all 0
timestamps like suggested in [2]
Please, use the data->timestamp as you suggested.
I'd suggest a bit of both. If you have a timestamp from the irq handler
use it. If it's not available then grab one locally in the threaded handler.
Hm. I don't think we will end up in the kx022a threaded handler so that
the data->timestamp is not populated in the IRQ handler. I am _far_ from
an IIO expert - but I guess the only way would be that some other
trigger invoked the threaded handler(?) Shouldn't the
kx022a_validate_trigger() prevent this?
Please, follow Jonathan's guidance if he does not tell othervice. You
clearly should not trust a random guy who obviously does not know how to
write these drivers in the first place XD
I hope that I'm understating this correctly or at least not totally
off :) If yes, I will send a patch.
Thanks Mehdi! I think this was a great catch! Maybe - while at it - you
could also send a patch adding a small kerneldoc to the
iio_trigger_poll_chained() mentioning this particular issue. Yes, I
guess it should be obvious just by reading the function name *_chained()
- but I did fall on this trap (and according to your reference [2] so
has someone else).
[1] https://lore.kernel.org/linux-iio/4FDB33CD.2090805@xxxxxxxxxx/
[2] https://lore.kernel.org/linux-iio/20201205182659.7cd23d5b@archlinux/
[3] https://lore.kernel.org/linux-iio/20220126191606.00003f37@xxxxxxxxxx/
Yours,
-- Matti
--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland
~~ When things go utterly wrong vim users can always type :help! ~~
