I'd like to add alert IRQ support to the lm63 driver. The new LM63 version, LM96163, no longer shares the same pin for both the tach input and the alert output, so it's quite a bit more useful. I've determined that with my prototype board that has an LM63, I can get either an alert IRQ or a tach input, without hardware modification. In order to get the IRQ all I need to do is not connect a 3-pin fan (or not connect the tach pin), as the tach signal effectively causes IRQs. My patch to let the lm63 fan be enabled/disabled via "fan1_enable" in sysfs has turned out to be quite useful, contrary to some claims that no one would ever use this feature. It's entirely possible to switch back and forth between tach and alert mode without rebooting. It looks like there aren't any hwmon drivers that support interrupts, despite it being a feature of virtually every hwmon chip. Is this correct, that there is no established way for dealing with the IRQs? Where should the code go? In platform code or in the lm63 driver? Which IRQ to request is platform specific, but actually doing so shouldn't be platform specific. The IRQ handler needs to somehow talk to the lm63, which if the handler is in platform code will be rather hard to do. The IRQ handler will need to read the lm63 alert (alarm in hwmon) status register to find out why the alert was generated (or _if_ an alert was generated, since there could be other chips in the same IRQ, for example I'll have two lm96163 chips with a common alert line). Reading the alert status register clears it if the alert condition no longer exists. This means there needs to be some communication between the IRQ handler and the lm63 driver so one doesn't prevent the other from seeing an alert bit. Suppose all that is worked out, how does the interrupt actually _do_ anything? The kernel could print a message, power off the system, change the processor speed or some other stuff. It would be nice to notify userspace somehow, but how? Cause a program to get run, like /sbin/hotplug (how about /sbin/toohotplug)? Send a signal to or wake a process blocked on one of the sysfs alarm files? I'm not sure how hard that is to do, but it does seem nice to be able to select() on temp2_max_alarm and then get woken when it changes. Or is there some other mechanism for this?
