Messages in this thread | | | Date | Mon, 08 Jun 2020 17:41:51 +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 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.
>> >> > > > 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)
>> > > > (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.
>> > > 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?
>> >> > But then, there is less use in duplicating the offsets in the MFD >> > just to have the MFD enumerate the subdevices and then match >> > the device tree nodes against it. I can just use >> > of_platform_populate() to enumerate the children and I won't >> > have to duplicate the base addresses. >> >> Which is fine. However this causes a different issue for you. By >> stripping out the MFD code you render the MFD portion seemingly >> superfluous. Another issue driver authors commonly contend with.
Yeah, I agree.
-michael
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