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SubjectRe: [PATCH v4 02/11] mfd: Add support for Kontron sl28cpld management controller
Am 2020-06-09 16:42, schrieb Mark Brown:
> On Tue, Jun 09, 2020 at 04:38:31PM +0200, Michael Walle wrote:
>
>> mfd-device@10 {
>> compatible = "simple-regmap", "simple-mfd";
>> reg = <10>;
>> regmap,reg-bits = <8>;
>> regmap,val-bits = <8>;
>> sub-device@0 {
>> compatible = "vendor,sub-device0";
>> reg = <0>;
>> };
>
> A DT binding like this is not a good idea, encoding the details of the
> register map into the DT binding makes it an ABI which is begging for
> trouble. I'd also suggest that any device using a generic driver like
> this should have a specific compatible string for the device so we can
> go back and add quirks later if we need them.

Like in the spidev case, yes. But OTOH if I _just_ encode the parameters
for the regmap a MFD, Lee don't agree because its just a shim. So either
way I seem to be stuck here.

Where should I put the code to create an i2c driver, init a regmap and
populate its childen?

-michael

>
>> ...
>> };
>>
>> Or if you just want the regmap:
>>
>> &soc {
>> regmap: regmap@fff0000 {
>> compatible = "simple-regmap";
>> reg = <0xfff0000>;
>> regmap,reg-bits = <16>;
>> regmap,val-bits = <32>;
>> };
>>
>> enet-which-needs-syscon-too@1000000 {
>> vendor,ctrl-regmap = <&regmap>;
>> };
>> };
>>
>> Similar to the current syscon (which is MMIO only..).
>>
>> -michael
>>
>> >
>> > I can't think of any reasons why not, off the top of my head.
>> >
>> > Does Regmap only deal with shared accesses from multiple devices
>> > accessing a single register map, or can it also handle multiple
>> > devices communicating over a single I2C channel?
>> >
>> > One for Mark perhaps.
>> >
>> > > > The issues I wish to resolve using 'simple-mfd' are when sub-devices
>> > > > register maps overlap and intertwine.
>> >
>> > [...]
>> >
>> > > > > > > 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.
>> >
>> > I see. Makes sense. This is board controller territory. Perhaps
>> > suitable for inclusion into drivers/soc or drivers/platform.

--
-michael

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