Re: [PATCH v3 1/8] soc: mediatek: Add PMIC wrapper for MT8135 and MT6397 SoC

[Flora Fu <flora.fu-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org>]

Hi,

On Tue, 2014-12-09 at 12:20 +0100, Arnd Bergmann wrote:
> On Tuesday 09 December 2014 11:30:15 Matthias Brugger wrote:
> > 2014-12-09 11:13 GMT+01:00 Sascha Hauer <s.hauer-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>:
> > > On Tue, Dec 09, 2014 at 09:23:18AM +0100, Arnd Bergmann wrote:
> > >>
> > >> I think we have had a similar case recently where a controller wasn't
> > >> actually using I2C, but the sofware protocol was close enough so we decided
> > >> to make it appear as i2c in Linux.
> > >>
> > >> Would that work for you, i.e. register the pmic wrapper as a fake spi
> > >> master driver in drivers/spi/ and register the rtc/regulator/codec
> > >> as SPI clients from DT?
> > >
> > > I don't think that's appropriate. I mean technically that could even
> > > work, but in software you really don't see anything from the underlying
> > > SPI bus. The SoC and the PMIC are really tightly coupled via the PMIC
> > > wrapper. This goes to the point where pins of the SoCs internal I2C and
> > > keypad controllers are routed over the SPI bus out of the PMIC. In
> > > software you do this by setting a bit in the I2C controller. If it's
> > > set, the signals are routed out of the PMIC instead of the main die.
> > > As said, technically we probably could create a fake SPI master, but
> > > that wouldn't really fit to this situation.
> 
> Ok, I see.
> 
> > I agree with Sascha. Although from the hardware point of view, the
> > communication between the PMIC and the SOC is done through SPI from
> > the point of view of the software everything looks like I2C commands
> > which will be "transalted" into SPI messages by the PMIC wrapper.
> 
> If it looks like i2c messages, would it be more appropriate to make
> it appear as an i2c controller then?


Although the message looks like I2C command, it is not I2C.
Form source code, the software does not touch any I2C i/o or protocols.
It depends SoC and has specific initial flow, read and write transfer
state. It is not able to an i2c controller.
That's why we consider its a proprietary hardware with specific
protocols. How about let it appear in driver/soc?

Thanks,
Flora

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