On Tue, Sep 06, 2022 at 08:36:25PM +0900, Hector Martin wrote: > On 06/09/2022 20.22, Linus Walleij wrote: > > On Tue, Sep 6, 2022 at 11:31 AM Mark Kettenis <mark.kettenis@xxxxxxxxx> wrote: > > > >> Another argument for having sub-nodes is that the firmware actually > >> exposes *two* GPIO controllers. For now we only support the "master" > >> PMU GPIOs, but there also is a "slave" PMU GPIO controller that uses a > >> separate set of SMC "keys". We currently don't need any of the pins > >> on the "slave", so we don't expose it in the DT yet. > > > > That sounds backward, like we don't expose device X as DT node > > because $OS doesn't use it yet. DT should just expose (by nodes or > > other ways) all hardware that exist or at least all hardware we know > > about no matter what $OS is using. > > How so? The are piles and piles of unused hardware not exposed in the > DT, and piles and piles of hardware that will be used but we haven't > figured out how to do it yet, so it's not exposed. For example, we know > there are like 8 or so UARTs, but we don't define them in the DT because > they are not connected to anything on any existing device and we don't > need them. Apple does the same thing in their DTs (only used hardware is > defined). > > I don't really see the point of exposing a GPIO controller when we don't > actually do anything with the pins yet, and might never do so. Having > drivers bind and stay unused just increases the amount of code running > without any ultimate purpose, so why do it? It's not like any other OS > would use the hardware either - GPIOs are only useful if they are > referenced in the DT for something, and we don't have anything that > would reference these. > > For SMC in particular, there's a huge amount of functionality we don't > have drivers for yet, and I don't see the point of trying to conjure up > DT bindings for it until someone writes a driver (and has a reason to do > so) :) Exposing in a DT is one thing. Defining in the binding is another. Even if it's not complete bindings, but just a fuller description of what functionality the MFD contains is. For example, just knowing there are 2 instances of GPIO, I'm much more inclined to agree GPIO should be a subnode. Rob
