On Mon, 08 Jun 2020, Andy Shevchenko wrote: > +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. Exactly. Because of the reasons in the paragraph above: "complex shared and sometimes intertwined batches of register sets to be consumed by multiple (sub-)devices spanning different subsystems" > > 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? > > > > > > > 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. > > > > > > > (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? > > > > > > 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'. > > > > 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. > > > > > 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. > -- Lee Jones [李琼斯] Senior Technical Lead - Developer Services Linaro.org │ Open source software for Arm SoCs Follow Linaro: Facebook | Twitter | Blog
