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

[ZHIZHIKIN Andrey]

Hello Fabio,

> -----Original Message-----
> From: Fabio Estevam <festevam at gmail.com>
> Sent: Friday, May 14, 2021 2:31 PM
> To: ZHIZHIKIN Andrey <andrey.zhizhikin at leica-geosystems.com>
> Cc: Peng Fan (OSS) <peng.fan at oss.nxp.com>; sbabic at denx.de; u-
> boot at lists.denx.de; uboot-imx at nxp.com; Ye Li <ye.li at nxp.com>
> Subject: Re: [PATCH 03/26] imx8mm_evk: Switch to new imx8mm evk board
> 
> 
> 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?

This would not be the only change that is necessary to provide support for both
ROMH and PCA PMIC ICs. From the commit, it seems that also the "duplication"
should be done in DTS and SPL PMIC code in power_init_board(void) should also
be adapted to get PMIC based on the config option.

I'm not saying it is not feasible - it is perfectly doable, but would require some
verification afterwards.

I can try to come up with the patch set for this but cannot commit to test the
change since I do not own a updated EVK board.

I guess an ideal situation would be that NXP can step in here to provide the better
version of this patch where both revisions are supported, and they can verify the
change on both EVK revisions.

> 
> Then we could have imx8mm_evk_defconfig for the new version and
> imx8mm_evk_rohm_defconfig for the old one.

Yes, ultimately this would be possible provided that both DTS and SPL code are
made in a way to provide implementation for both PMIC types.

> 
> What do you think?
> 
> Thanks

-- andrey