[U-Boot] [RFT 1/8] exynos: Redo detection of revision when all resources are ready

[Lukasz Majewski <lukma@denx.de>]

Hi Krzysztof,

> On Mon, 11 Feb 2019 at 08:20, Lukasz Majewski <lukma@denx.de> wrote:
> >
> > Hi Krzysztof,
> >  
> > > Detection of board type is done early - before power setup.  In
> > > case of Odroid XU3/XU4/HC1 family, the detection is done using
> > > ADC which is supplied by LDO4/VDD_ADC regulator.  This regulator
> > > could be turned off (e.g. by kernel before reboot);  If ADC is
> > > used early, the regulators are not yet available and the
> > > detection won't work.
> > >
> > > Try to detect the revision again, once power is brought up.
> > >
> > > This is necessary to fix the detection of Odroid HC1 after
> > > reboot, if kernel turned off the LDO4 regulator.  Otherwise the
> > > board is not detected....  
> >
> > But such approach seems not to be the optimal one (as we perform
> > detection twice - with default LDO4 enabled after power on and after
> > soft reset).
> >
> > I would expect to enable the LDO4 regulator in the early code (I2C
> > would be probably necessary) and then read ADC value properly once.
> >
> > (I also guess that the "work-by-chance" approach is caused by
> > default settings of PMIC after power on).  
> 
> So basically you want to move the board detection after the
> exynos_power_init()... maybe it is possible. The other way is to split
> set_board_type() into OF part (for compatible and main board
> difference) and revision detection (requiring ADC). Maybe it is
> possible, but isn't it used before?

I do want to avoid making the detection twice;

First time when we have the LDO4 enabled by default and the second time
when it may happen that we do a soft reset from Linux (which disabled
LDO4).

> 
> > As fair as I remember, TI is able to read the EEPROM via I2C in the
> > very early u-boot (MLO to be precise) code and then make the
> > decision regarding the platform.
> >
> > Maybe it would be possible to do the same with Samsung?
> >
> > And another thought - if the set_board_type() can be called latter
> > and it works - why cannot we move it to this latter point and
> > execute exactly once?  
> 
> It is the same as previous idea... or I do not see the difference...
> 
> Best regards,
> Krzysztof




Best regards,

Lukasz Majewski

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