User Space GPIO Interrupt programming - GSoC-2018

[Ian Lepore]

On Fri, 2020-11-27 at 10:16 -0700, Ian Lepore wrote:
> On Fri, 2020-11-27 at 14:28 +0300, Vladimir Goncharov wrote:
> > Here it is.
> > There is struct gpioc_event with pin number and bintime which is send
> > to userspace.
> > 
> > Also I'm thinking about to implementation notofication without extra
> > reading from socket via struct kevent's extra fields (fflags/ext[4]),
> > looks like it is possible.
> > 
> 
> Please don't top-post on freebsd mailing lists.
> 
> I think we need a way for the app to choose whether it wants simple
> reporting of pin number (like the original code) perhaps along with a
> count, versus requesting detailed per-event data.  I'm going to propose
> something more detailed about this as soon as I get my thoughts all
> organized.  I also want to get the original code and the locking fixes
> I've done to it into a phab review for people to start looking at
> before starting to do new major changes to it.
> 
> Allocating memory in the interrupt handler isn't a good idea, it will
> just increase latency on processing other pin interrupts and lead to
> inaccurate timestamps.  IMO, it would be better to allocate a fixed
> array of events; when the app requests detailed event reporting it can
> request the number of stored events it wants handled and we could
> allocate all at once based on that.
> 

The gsoc2018 code, with locking and style(9) fixes, is now at:

  https://reviews.freebsd.org/D27398

-- Ian