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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