On Wednesday 16 July 2014 12:34:56 Olof Johansson wrote: > On Wed, Jul 16, 2014 at 11:57 AM, Thierry Reding > <thierry.reding@xxxxxxxxx> wrote: > > On Wed, Jul 16, 2014 at 05:22:03PM +0200, Arnd Bergmann wrote: > >> On Wednesday 16 July 2014 17:14:29 Thierry Reding wrote: > >> > > > >> > > Ok, I'll have a look. I think when this becomes a separate driver, it > >> > > should also have its own header file, so maybe you can in the meantime > >> > > make it a local header file in mach-tegra until we have found a good > >> > > place for it. > >> > > >> > Why do you think it should be a separate header? We already have a > >> > couple in include/linux and I'm not sure it's useful to add even more. > >> > If anything I would've thought it made sense to move the content of the > >> > other headers into tegra-soc.h. > >> > >> I very much dislike the idea of having a per-vendor header file that > >> everything gets crammed into. We should try to have proper subsystems > >> and generic interfaces for these wherever possible. > > > > I completely agree. However spreading the SoC-specific functions across > > multiple header files isn't going to help. If we keep all the per-vendor > > APIs in one file it makes it easier to see what could still be moved off > > into a separate subsystem. > > > > Now for PMC specifically, we've investigated converting the powergate > > API to power domains. I don't think it will be possible to make that > > work. The issue is that there's a defined sequence that needs to be > > respected to make sure the device is powered up properly. That sequence > > involves the primary clock and reset of the device. It's been proposed > > to make these clocks available to the PMC driver so that it can control > > them, but then we can't make sure that clocks are really off if they > > need to be, since we have two drivers accessing them. The only way I see > > to make that work reliably is by moving complete control of the > > powergate into drivers so that they can make sure clocks and resets are > > in the correct states. I don't completely follow, but that's ok ;-) > > The PMC driver also provides access to I/O rails and specifically a deep > > power down state. Some modules are in deep power down state by default, > > so they need to be brought out of that state. I suppose this would be > > easier to turn into a generic framework because there aren't any cross- > > dependencies like for powergates, but I'm not aware of any other SoC > > having a similar feature (or implementation thereof in the kernel). And > > adding a subsystem just for the sake of it if only one implementation is > > available isn't a good idea in my opinion because it will be naturally > > designed to work best (and therefore maybe only) for the one instance. > > > > This issue is a fundamental one and there are bound to be other SoCs > > that have similarly unique blocks for which it's impractical to add a > > framework. I suspect the primary reason why we haven't run into it this > > frequently is because a lot of it is still hidden in arch/arm/mach-*. > > > > I'm open to suggestions of course, but the best option I currently see > > is to collect these custom APIs in a central place so that we can easily > > compare various SoCs for commonalities as time goes by and factor them > > out into subsystems where appropriate. > > > > For the same reason I think it's valid to put this type of code into > > drivers/soc. That way we have one subdirectory to look through for > > potential unification rather than various ones sprinkled across arch > > directories. It makes little sense in my opinion to move this code to > > drivers/power if there's no common framework anyway. > > I agree. We can move them out and make them common them later if needed. > > We're sometimes trying too hard to find proper homes for various new > drivers, which means that we're proliferating the kernel with a lot of > new driver directories that have only one or two drivers in them. > > I'd rather collect stuff in drivers/soc, and move it out as needed > later. Especially since we merge drivers/soc through one merge path > (arm-soc) and can keep an eye on it, while the > scatter-drivers-everywhere approach merges through various > maintainers. Ok. I'm fine with having one driver in drivers/soc for the pmc (and a few associated bits if necessary) and a header file for that. If you end up with two separate drivers in drivers/soc, I'd also prefer two separate header files. It may be a good idea to put these headers somewhere other than include/linux/*.h, which is completely overloaded by random stuff. We could use include/linux/soc/*.h or include/soc/*.h for those. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
