i2c bit banging timeout for SCL

[Warner Losh]

On Mon, Jul 1, 2019 at 11:14 AM Poul-Henning Kamp <phk at phk.freebsd.dk>
wrote:

> --------
> In message <
> CANCZdfoFBvmxPtnEL4GOqXTvp6Zd-xrtja4rmUO1rAcy0JdeSw at mail.gmail.com>,
> Warner Losh writes:
>
> >The only issue, really, is that this timeout is a busy loop and there may
> >be I/O bus contention introduced on these systems.
>
> Does it have to be a busy loop for the entire duration ?
>
> Spin for the median, timeout+poll for the rest of the time ?
>

That's a good suggestion. I'd be inclined to spin for 1 tick or so, then do
a timeout per tick after that (eg, shift from DELAY to pause(1)). It won't
be super accurate or high performance, but when the devices are slow, that
would add only a little extra time.

Ideally, that's what we'd do. In the short term, bumping the timeout
wouldn't be horrible.

Warner