On Wed, Jul 16, 2014 at 12:31:00PM -0700, Olof Johansson wrote: > [ Gee, I had completely missed this thread because nobody bothered to > cc me. Seems to be standard procedure on 64-bit these days. :( ] > > > On Mon, Jun 30, 2014 at 12:20 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Saturday 28 June 2014 22:40:26 Thierry Reding wrote: > >> > > pmc.c implements various routines to access the power management > >> > > controller, some of which is needed by suspend/resume, some of it is > >> > > needed by SMP. powergate.c implements a subset of the PMC that needs to > >> > > be exported to drivers to enable power partitions on the SoC. I'm not > >> > > aware of subsystems that deal with this kind of driver. > >> > > > >> > Please see above. > >> > >> Like I said, I don't see what business suspend/resume related code has > >> in drivers/power. What we're talking about here really is functionality > >> very specific to Tegra. Also some of that code needs to be run at very > >> early points in the boot process, so we can't reasonably turn it into a > >> proper driver anyway. > > > > I believe the powergate.c stuff can be changed into pm_domain code, but > > we don't have a good subsystem with generic DT bindings yet, so that > > may need some more groundwork first. drivers/power or a subdirectory > > of that may end up being the right place though. > > > >> Also, the real win we get from moving code out into drivers/ is if we > >> can provide a common framework for them. I don't see how we can possibly > >> do that for this code since there simply isn't enough commonality > >> between SoCs. At the same time we now have a situation where both 32-bit > >> and 64-bit variants of some SoCs share some of the same hardware at the > >> very low level and since we don't have mach-* directories for 64-bit ARM > >> and shouldn't be duplicating code either, we need to find a new home for > >> this type of code. drivers/soc seemed to fit perfectly well. > > > > For the low-level stuff yes, but I agree with Santosh there needs to be > > some more work trying to split out individual high-level drivers. > > > > There are two common patterns for the interface between the low-level > > register access and the more high-level stuff: you can either use > > a "syscon" driver that just exports a struct regmap and that gets referenced > > from other drivers using a phandle in their device nodes, or you have > > a driver in drivers/soc that exports a somewhat higher-level interface > > and comes with its own header file that gets included by other drivers. > > At the moment, the syscon/regmap variant can only be used once device > > drivers are loaded, but there is some broad agreement that it should > > be changed to allow calling syscon_regmap_lookup_by_phandle() at > > early boot using just DT accessors. > > I'd strongly prefer to NOT tie this into DT and keep it as in-kernel > implementation until we know more what a common subsystem might look > like, if any. > > If we keep it only in the kernel, then we're free to change it as > needed. If we tie it into DT/syscon, then we get stick with > stable-only ABIs from day one. That doesn't seem like a good idea. There are two sides to keeping to an in-kernel API too: it may seem like we're free to change this at will and aren't subject to a stable ABI. However that's not entirely accurate. Assume we don't put any information about a feature into DT but use an in-kernel API only. Once we've come up with a good way to represent that in DT and have a generic framework that we can use, we'll most likely still need to keep around the old API in the kernel to make sure the kernel still works with a DT that doesn't have nodes and/or properties for the new binding. So the question arises: at that point is it really worth using a DT binding? Since we already have an API that works, why bother coming up with a new one? Especially if we can't get rid of the one we already have anyway? Thierry
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