On Fri, Dec 30, 2016 at 4:15 PM, Jonathan Cameron <jic23@xxxxxxxxxx> wrote: > On 30/12/16 13:05, Linus Walleij wrote: >> So this needs to be re-architected to either describe the remote system >> in DT and handle it in the kernel, or handle it all from userspace if it >> is a one-off non-product thing. > > I'm not sure this is always true (though it might be here). There is always > a need to describe the edge of the known world. Be it that we have > an accelerometer - ultimately we could describe the device generating the > acceleration but we have no way of knowing what it is or what it will do.. > > What we have here is a rather simple case, but what about an I/O bank on > a PLC. Obviously we can handle that as a bunch of GPIOs but if we know > more about it we should have means to describe that. Say we know they are > always driving relays, we should be able to describe that additional known > stuff. Relays have characteristics such as bounce times etc that if described > would allow us to do the relevant filtering on inputs to handle this. > > Here the fact it is a power supply switch should be describable. Hard to > get right in a generic way though so in cases like this perhaps you > are right and it should just be left undescribed and handled in userspace. > > Anyhow, here I think leaving it as a gpio interface is probably the way to > go, but I'm not sure that will always be the case. No you are right. We are at the fuzzy system perimeter. For GPIO we currently only have asserted/unasserted, polarity of that, open drain/source and debounce time. But we will need the whole slew of pin control settings in the future: drive strength, schmitt-trigger hysteresis etc etc. And if there is a further component beyond that it may need a driver in turn even if it is "only" a relay. Let's see about this one... Yours, Linus Walleij -- 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
