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

[Alan Kay]

Hi Lukasz,

On Mon, Oct 9, 2023 at 8:49 AM Lukasz Majewski <lukma at denx.de> wrote:
>
> Hi Fabio, Alan,
>
> > Hi Alan,
> >
> > [Adding Lukasz and Cody]
> >
> > On Tue, Aug 30, 2022 at 2:49 PM Alan Kay <alan at 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 at 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
>
> --
>
> DENX Software Engineering GmbH,      Managing Director: Erika Unter
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
> Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma at denx.de

The patch:
https://source.denx.de/u-boot/u-boot/-/commit/79230640cb4fb780e2be9bb9a47b31976b18cac4
does fix the issue, please feel free to discard my patch, thank you.

Best regards,
Alan Kay