On Mon, 08 Jun 2020, Michael Walle wrote: > Am 2020-06-08 12:02, schrieb Andy Shevchenko: > > +Cc: some Intel people WRT our internal discussion about similar > > problem and solutions. > > > > On Mon, Jun 8, 2020 at 11:30 AM Lee Jones <lee.jones@xxxxxxxxxx> wrote: > > > On Sat, 06 Jun 2020, Michael Walle wrote: > > > > Am 2020-06-06 13:46, schrieb Mark Brown: > > > > > On Fri, Jun 05, 2020 at 10:07:36PM +0200, Michael Walle wrote: > > > > > > Am 2020-06-05 12:50, schrieb Mark Brown: > > > > ... > > > > > Right. I'm suggesting a means to extrapolate complex shared and > > > sometimes intertwined batches of register sets to be consumed by > > > multiple (sub-)devices spanning different subsystems. > > > > > > Actually scrap that. The most common case I see is a single Regmap > > > covering all child-devices. > > > > Yes, because often we need a synchronization across the entire address > > space of the (parent) device in question. > > > > > It would be great if there was a way in > > > which we could make an assumption that the entire register address > > > space for a 'tagged' (MFD) device is to be shared (via Regmap) between > > > each of the devices described by its child-nodes. Probably by picking > > > up on the 'simple-mfd' compatible string in the first instance. > > > > > > Rob, is the above something you would contemplate? > > > > > > Michael, do your register addresses overlap i.e. are they intermingled > > > with one another? Do multiple child devices need access to the same > > > registers i.e. are they shared? > > No they don't overlap, expect for maybe the version register, which is > just there once and not per function block. Then what's stopping you having each device Regmap their own space? The issues I wish to resolve using 'simple-mfd' are when sub-devices register maps overlap and intertwine. > > > > > > But, there is more in my driver: > > > > > > (1) there is a version check > > > > > > If we can rid the Regmap dependency, then creating an entire driver to > > > conduct a version check is unjustifiable. This could become an inline > > > function which is called by each of the sub-devices instead, for > > > example. > > sounds good to me. (although there would then be a probe fail per sub-device > if the version is not supported) I don't see an issue with that. I would put that check inside a shared call though, complete with support for locking. > > > > > > (2) there is another function for which there is no suitable linux > > > > > > subsystem I'm aware of and thus which I'd like to us sysfs > > > > > > attributes for: This controller supports 16 non-volatile > > > > > > configuration bits. (this is still TBD) > > > > > > There is a place for everything in Linux. > > > > > > What do these bits configure? > > - hardware strappings which have to be there before the board powers up, > like clocking mode for different SerDes settings > - "keep-in-reset" bits for onboard peripherals if you want to save power > - disable watchdog bits (there is a watchdog which is active right from > the start and supervises the bootloader start and switches to failsafe > mode if it wasn't successfully started) > - special boot modes, like eMMC, etc. > > Think of it as a 16bit configuration word. And you wish for users to be able to view these at run-time? Can they adapt any of them on-the-fly or will the be RO? > > > > > TBH I'd also say that the enumeration of the subdevices for this > > > > > device should be in the device rather than the DT, they don't > > > > > seem to be things that exist outside of this one device. > > > > > > > > We're going circles here, formerly they were enumerated in the MFD. > > > > Yes, they are devices which aren't likely be used outside a > > > > "sl28cpld", but there might there might be other versions of the > > > > sl28cpld with other components on different base addresses. I > > > > don't care if they are enumerated in DT or MFD, actually, I'd > > > > prefer the latter. _But_ I would like to have the device tree > > > > properties for its subdevices, e.g. the ones for the watchdog or > > > > whatever components there might be in the future. > > > > > > [...] > > > > > > > MFD core can > > > > match a device tree node today; but only one per unique compatible > > > > string. So what should I use to differentiate the different > > > > subdevices? > > > > > > Right. I have been aware of this issue. The only suitable solution > > > to this would be to match on 'reg'. > > see below (1) > > > > > > > FYI: I plan to fix this. > > > > > > If your register map needs to change, then I suggest that this is > > > either a new device or at least a different version of the device and > > > would also have to be represented as different (sub-)mfd_cell. > > > > > > > Rob suggested the internal offset, which I did here. > > > > > > FWIW, I don't like this idea. DTs should not have to be modified > > > (either in the first instance or subsequently) or specifically > > > designed to patch inadequacies in any given OS. > > How does (1) play together with this? What do you propose the "reg" > property should contain? Whatever is in the 'reg' property contained in the Device Tree node. Either the full address or an offset would be suitable. Caveat: All this thinking has been done on-the-fly. I would need to look at some examples of existing devices and start coding before I could really think the solution through. Happy to discuss and/or take recommendations though. -- Lee Jones [李琼斯] Senior Technical Lead - Developer Services Linaro.org │ Open source software for Arm SoCs Follow Linaro: Facebook | Twitter | Blog
