Re: A case of watchdog+LED shared GPIO pin

[Pavel Machek <pavel@ucw.cz>]

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Hi!

> We (the development team at my current employer company) are having a
> specific case of hardware configuraton. Namely, the same GPIO pin is
> used for both watchdog keepalive signaling and status LED blinking.
> The thing is, there are multiple blinking frequency modes for this
> LED, each with its own meaning (i.e. system/firmware states), so
> there's a need for changing the frequency/period dynamically from
> userspace.
> 
> Previously I've done the thing implementing the timer period
> configuration by updating a special sysfs file with new values in the
> gpio_wdt driver. However since recently (commit 03bca15 in the kernel
> Git repo) the timer has been swapped out with the keepalive callback
> thing, which, as far as I can tell, supports updating the timeout
> period via the WDIOC_SETTIMEOUT ioctl. However this ioctl is
> insufficient for our purposes, in the sense that its minimum
> resolution is 1 whole second, while we need a 100 millisecond
> granularity at the very most.
> 
> I could also simply disable the gpio_wdt altogether and just use a LED
> trigger driven configuration, but I highly doubt this would be a wise
> thing, since the whole point of the watchdog is monitoring
> responsiveness of the userspace. Also I gather that controlling the
> GPIO entirely from a userspace process is rather undesirable, too, as
> it might lead to confusing latencies sometimes, for a start.
> 
> I'd like to hear your opinions on the preferred way(s) of implementing
> this for our product hardware on the most recent kernels, which could
> be sent to upstream to secure further backwards compatibility.

Improving WDIOC_SETTIMEOUT is obvious solution. I'd go for that.

But actually, controlling GPIO entirely from userspace should work
well, too. User is not going to notice the jitter in miliseconds...

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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