linux-kernel - Re: [PATCH v7 1/6] DONOTMERGE: arm64: dts: ti: Add TI TPS65219 PMIC support for AM642 SK board.

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Message-ID: <Y5tl3+2pJispcXy6@sirena.org.uk>
Date:   Thu, 15 Dec 2022 18:22:23 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Nishanth Menon <nm@...com>
Cc:     jerome Neanne <jneanne@...libre.com>,
        Wadim Egorov <W.Egorov@...tec.de>,
        "lgirdwood@...il.com" <lgirdwood@...il.com>,
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Subject: Re: [PATCH v7 1/6] DONOTMERGE: arm64: dts: ti: Add TI TPS65219 PMIC
 support for AM642 SK board.

On Thu, Dec 15, 2022 at 11:54:11AM -0600, Nishanth Menon wrote:
> On 16:09-20221215, Mark Brown wrote:

> > That proposal looks really non-idiomatic and quite unusual, if there's a
> > fixed voltage supply to the LDO I'd expect to see it modeled as a fixed
> > voltage regulator.  I'm not sure what the use of bypass here is trying
> > to accomplish TBH.

> The problem is this - the default NVM in the PMIC is setup such that
> VSET value =3.3v and bypass bit set (makes sense since the vin=3.3v).

This implies no voltage drop over the LDO?  Sounds a bit suspect.

> Now the constraint is bypass bit cannot be changed without the LDO
> being switched off.

> regulator-allow-bypass property allows us to control bypass bit, but we
> should'nt toggle it when LDO is active. Not providing the property
> implies the bit wont be toggled by regulator core either.

> What we need is a scheme that will disable the bypass bit with the
> intent of operating the LDO with just the vset field. I did'nt find it
> possible atm.. unless I am mistaken..

Can the consumer just disable the supply as part of startup?  Though
that's starting to feel rather board specific.  There's not really a
good place to put a board specific setup process like that in the kernel
at the minute, you'd ideally want the firmware to leave the device at
least disabled if not actually out of bypass on startup so we don't have
to deal with this.  Ugh...

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