Re: [RFC PATCH] mxs: Don't enable 4P2 reg if mx28 is powered only from DCDC_BATT without 5V

[Lukasz Majewski <lukma@denx.de>]

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Hi Fabio, Alan,

> Hi Alan,
> 
> [Adding Lukasz and Cody]
> 
> On Tue, Aug 30, 2022 at 2:49 PM Alan Kay <alan@londelec.com> wrote:
> >
> > mxs_power_enable_4p2() was added to mxs_batt_boot() in
> > 'commit a0f97610757d ("ARM: mxs: Enable DCDC converter for battery
> > boot")' to enable DCDC converter when board is powered from 5V and
> > has detected sufficient battery voltage.
> > This involves enabling 4P2 regulator and there is a code
> > in mxs_power_enable_4p2() that disables VDDIO, VDDA, VDDD outputs of
> > the DCDC converter and enables BO for each power rail e.g.
> >
> >         setbits_le32(&power_regs->hw_power_vddioctrl,
> >                 POWER_VDDIOCTRL_DISABLE_FET |
> > POWER_VDDIOCTRL_PWDN_BRNOUT);
> >
> > In case the mx28 is powered by the 5V source and linear regulators
> > are supplying power to the VDDIO, VDDA, VDDD rails there is no
> > issue.
> >
> > However if the mx28 is powered by the DCDC_BATT source only without
> > 5V, disabling the DCDC converter outputs causes brownout power down.
> >
> > The proposed solution is not to call mxs_power_enable_4p2() at all
> > if the mx28 is powered by the DCDC_BATT source only. There is no
> > reason to enable 4P2 regulator in this case and setup of all
> > registers is done in mxs_batt_boot().
> >
> > Also there is no need to enable 5V brownout in
> > mxs_power_init() in this case.
> >
> > Please consider if this is acceptable and I will submit a proper
> > patch.
> >
> > Signed-off-by: Alan Kay <alan@londelec.com>  
> 
> Cody also sent a fix for this issue:
> 
> https://patchwork.ozlabs.org/project/uboot/patch/20230703163340.101490-2-cody@londelec.com/

Isn't this already addressed with:
https://source.denx.de/u-boot/u-boot/-/commit/79230640cb4fb780e2be9bb9a47b31976b18cac4

Please also look into the recent patches for imx287 (xea board for
reference):

tig -- arch/arm/cpu/arm926ejs/mxs/spl_power_init.c

At least SHA1: 65b9b3462bec2966911658836983819ab4e4823e


Best regards,

Lukasz Majewski

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