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SubjectRe: [PATCH v4 02/11] mfd: Add support for Kontron sl28cpld management controller
Am 2020-06-09 08:47, schrieb Lee Jones:
> On Mon, 08 Jun 2020, Michael Walle wrote:
>
>> 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?
>
> Not sure what (if any) the restrictions are.

You can only have one device per I2C address. Therefore, I need one
device
which is enumerated by the I2C bus, which then enumerates its
sub-devices.
I thought this was one of the use cases for MFD. (Regardless of how a
sub-device access its registers). So even in the "simple-regmap" case
this
would need to be an i2c device.

E.g.

&i2cbus {
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>;
};
...
};

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.

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