On Tue, Jan 10, 2017 at 11:41:44AM -0600, Benjamin Herrenschmidt wrote: > On Sat, 2017-01-07 at 09:15 -0800, Guenter Roeck wrote: > > > Instead of the "online" attribute, what do you think about using the > > > "bind"/"unbind" API to probe the device from user space once the system > > > is powered on? All the hwmon registration would take place in the probe > > > function, it would just occur some time after boot. > > > > > > > A more common approach would be to have a platform driver. That platform > > driver would need a means to detect if the OCC is up and running, and > > instantiate everything else once it is. > > > > A trigger from user space is problematic because there is no guarantee > > that the OCC is really up (or that it even exists). > > > > An alternative might be to have the hwmon driver poll for the OCC, > > but that would be a bit more difficult and might require a kernel thread > > or maybe asynchronous probing. > > Hi Guenter ! > > I'm not sure I agree with you here ;-) > > I'm don't know how much background you got (I missed the beginning of > the discussion) but basically this driver runs on the BMC (system > controller) of the POWER9 server, the OCC is inside the POWER9 chip > itself. > > So the presence/power state of the OCC doesn't depend on the BMC > platform kernel code. The BMC userspace controls power up and down to the POWER9, and thus it's the one to know whether the remote is up. > > If we were to create a "platform driver", all it would do is get input > from userspace exactly like that sysfs file :-) > > So if you don't like the sysfs file that registers/de-registers, which > I sort-of understand, it's a bit of a hack (though a rather efficient > one), I think the bind/unbind approach makes sense. However, I wonder > whether the simplest and most efficient (remember this BMC has a really > slow CPU) is an "online" file sysfs file, though rather than > registering/de-registering the hwmon it would simply make it stop > accessing the HW (and return some known "offline" values). > I don't like that too much either; it still looks like a hack. How about using bind/unbind then ? Guenter -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
