Messages in this thread | | | Date | Mon, 08 Jun 2020 23:09:01 +0200 | From | Michael Walle <> | Subject | Re: [PATCH v4 02/11] mfd: Add support for Kontron sl28cpld management controller |
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Am 2020-06-08 20:56, schrieb Lee Jones: > 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@linaro.org> 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?
Because its just one I2C device, AFAIK thats not possible, right?
> 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?
And esp. change them.
> Can they adapt any of them on-the-fly or will the be RO?
They are R/W but only will only affect the board behavior after a reset.
-michael
> >> > > > > 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.
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