On Thu, 19 Jul 2018, at 04:37, Rob Herring wrote: > On Tue, Jul 17, 2018 at 5:28 PM Andrew Jeffery <andrew@xxxxxxxx> wrote: > > > > On Tue, 17 Jul 2018, at 14:26, Benjamin Herrenschmidt wrote: > > > On Mon, 2018-07-16 at 07:55 -0600, Rob Herring wrote: > > > > If that data is one set per SoC, then i'm not that concerned having > > > > platform-specific data in the driver. That doesn't mean the driver is > > > > not "generic". It's still not clear to me in this thread, how much of > > > > this is board specific, but given that you've placed all the data in > > > > an SoC dtsi file it seems to be all per SoC. > > > > > > So Rob, I think that's precisely where the disconnect is. > > > > > > I think we all (well hopefully) agree that those few tunables don't fit > > > in any existing subystem and aren't likely to ever do (famous last > > > words...). > > > > > > Where we disagree is we want to make this parametrized via the DT, and > > > you want us to hard wire the list in some kind of SoC driver for a > > > given SoC family/version. > > > > > > The reason I think hard wiring the list in the driver is not a great > > > solution is that that list in itself is prone to variations, possibly > > > fairly often, between boards, vendors, versions of boards, etc... > > > > > > We can't know for sure every SoC tunable (out of the gazillions in > > > those chips) are going to be needed for a given system. We know which > > > ones we do use for ours, and that's a couple of handfuls, but it could > > > be that Dell need a slightly different set, and so might Yadro, or so > > > might our next board revision for that matter. > > > > > > Now, updating the device-tree in the board flash with whatever vendor > > > specific information is needed is a LOT easier than getting the kernel > > > driver constantly updated. The device-tree after all is there to > > > reflect among other things system specific ways in which the SoC is > > > wired and configured. This is rather close... > > > > Not sure this helps, but I feel that the proposal pretty closely matches what's described in Documentation/devicetree/bindings/mfd/mfd.txt. It's intended that nodes using the bindings I'm proposing are children of a 'compatible = "syscon", "simple-mfd"' node (this is the case with the features we're hoping to describe for our SoC). I should explicitly call that out. > > IMO, any binding that has only those compatibles is not correct and a > specific compatible is needed. We should be able identify a specific > h/w block. I didn't intend for that to get interpreted quite as literally, so apologies for that. We do have h/w-block-specific compatibles in there too. The point was to demonstrate that we're dealing (at this point, only) with mfds/syscons. > > > But to go on, "simple-mfd" is effectively an alias of "simple-bus", which means its intended to match child node compatibles to drivers provided by the kernel. If we shouldn't be describing minor features of a SoC in the devicetree, doesn't this invalidate the case for simple-mfd? What is the *correct* use of simple-mfd? When is it not used to expose minor features in set of "miscellaneous system registers"? Why doesn't this proposed case fit? > > I'm no fan of simple-mfd either. I think it is abused and often a sign > of bad binding design. Ah, yes, this is a familiar feeling when reflecting on things I've done in the past. Hence trying to understand how to use it right. > The general problem with MFD bindings is people > define child nodes based on what drivers they happen to have for some > OS. DT is not the only way to instantiate drivers. Child nodes are > really only needed when you have resources per child that need to be > defined. For example, if the MFD has an interrupt controller and > interrupts to sub-blocks or sub-blocks have their own clocks. > "simple-mfd" was for when the parent node has no driver or the child > nodes have no dependency on the parent. Thanks for the clarification, I'll keep that in mind going forward. Andrew -- 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
