[PATCH 03/26] imx8mm_evk: Switch to new imx8mm evk board

Ricardo Salveti rsalveti at rsalveti.net
Fri May 14 17:29:02 CEST 2021

Hi Fabio,

On Fri, May 14, 2021 at 9:30 AM Fabio Estevam <festevam at gmail.com> wrote:
> Hi Andrey,
> On Wed, May 12, 2021 at 6:47 PM ZHIZHIKIN Andrey
> <andrey.zhizhikin at leica-geosystems.com> wrote:
> > > Update PMIC to use PCA9540, the legacy board not supported by NXP
> >
> > This commit seems rather a "nuclear" to me, as de-facto it drops the initialization of ROMH PMIC in
> > favor of PCA one, leaving all the previous board revisions not to be properly sourced.
> >
> > I know that there might be no intention to provide a support for earlier revisions of i.MX8M Mini
> > EVKs from NXP, but providing no backward compatibility to those boards which are still in use by
> > a lot of people for development purposes is highly undesirable either.
> >
> > TBH, I've tested this patch on the old EVK where ROMH PMIC is present, and apart from having some
> > error messages in SPL regarding the register writes - it does boots. What worries me the most though
> > is that DTS changes some voltage settings, which I'm not sure how the SOC would react on.
> >
> > To my opinion, this patch should either be complemented with the mechanism to provide a
> > level of backward compatibility (where the PMIC can be dynamically identified and instantiated),
> > or the separate implementation should be presented which would make the old board type not to
> > be bootable at all if it is considered not to be supported any longer. Or this patch should be reverted
> > in an effort to come up with a solution which covers new revision without "damaging" the currently
> > integrated one.
> >
> > Fabio / Stefano,
> > Do you have any thoughts here on how this should be handled further, considering the fact that the
> > backward compatibility of 2021.07 release is not kept for this board type across multiple revisions?
> >
> > I'd really like to get your opinion here as I do have those boards in development and would need to
> > come up with the idea on what to do with them.
> >
> > Also, this should be taken care of in the Yocto, since there is only one definition of the i.MX8MM EVK
> > machine which does not make any distinction regarding the revision.
> You bring a good point.
> What about adding a new defconfig to support the old imx8mm-evk with
> the Rohm PMIC?
> Then we could have imx8mm_evk_defconfig for the new version and
> imx8mm_evk_rohm_defconfig for the old one.
> What do you think?

Maybe a dynamic way to identify if BD71837 or PCA9450 (by probing i2c)
would work better?

Different configs would imply different builds and binaries, which is
a problem when trying to support a single build for both the old EVK
and EVKB (and the main difference is the PMIC, nothing really major).

I also share Andrey's concerns, as we do have several EVKs in hands,
and having one single build would facilitate quite a bit.

Ricardo Salveti de Araujo

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