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: <b6ea8cb7-38c4-13cf-a08a-ece973859342@ti.com>
Date:   Fri, 16 Dec 2022 11:51:28 +0530
From:   Vignesh Raghavendra <vigneshr@...com>
To:     Nishanth Menon <nm@...com>, Mark Brown <broonie@...nel.org>
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 16/12/22 03:11, Nishanth Menon wrote:
> On 18:22-20221215, Mark Brown wrote:
>> 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.
> 
> Not the choice I'd probably have made ;)
> 
>>
>>> Now the constraint is bypass bit cannot be changed without the LDO
>>> being switched off.
>>

Per https://www.ti.com/lit/ds/symlink/tps65219.pdf (7.3.6 Linear
Regulators).

LDOs have two modes:

1. Load switch mode: in this case, output voltages of 1.5V up to 5.5V
are supported.

2 Linear regulator LDO mode where output voltage is programmable in the
range of 0.6V to 3.4V in 50mV-steps with possibility of bypass.

(CAUTION on page 25):
A mode change between LDO(/bypass) and LSW-mode must only be performed,
when this regulator is disabled!
A change between LDO and bypass-mode (supported by LDO1 and LDO2 only)
is supported during operation.

So, seems like bypass can be toggled even with LDO on?



[...]

Regards
Vignesh