[Linux-stm32] Counter device Interface for reading out input capture

[Ahmad Fatoum]

Hello William,

On 06.11.20 13:42, William Breathitt Gray wrote:
> On Thu, Nov 05, 2020 at 07:46:14PM +0100, Ahmad Fatoum wrote:
>> It doesn't look like the counter device API is yet made to support such
>> an input capture mode (latching a counter value on an external event, e.g.
>> to timestamp incoming rising edges to measure jitter between pulses).
>
> Regarding the Counter subsystem, I'm developing a Counter character
> device API that supports timestamps for counter devices:
> https://lore.kernel.org/linux-arm-kernel/157d1edf-feec-33b5-7ad5-94f99316ca6e@lechnology.com/T/

Any chance we could have a "raw" timestamp as well like the network
stack offers (cf. SOF_TIMESTAMPING_{RAW,SYS}_HARDWARE)?

The API currently only exposes a ktime (i.e. CLOCK_MONOTONIC), which the
raw timer count can't be readily converted to. For our use case of
measuring jitter, the raw value is sufficient.

> My aim is to get this functionality picked up for the Linux 5.11 merge
> window. I have one more revision at least that should be ready in a
> couple weeks -- I'll CC you for that patchset to keep you in the loop;
> I force-push periodically to my personal repo when as I develop, so you
> can take a look at the current state of this next revision if you're
> curious:
> https://gitlab.com/vilhelmgray/iio/-/tree/counter_chrdev_v6

Great. Looking forward to see this merged.

Thanks,
Ahmad

> 
> Sincerely,
> 
> William Breathitt Gray
> 

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