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From: "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
Date: Thu, 6 Jun 2024 15:12:42 +0100
Message-ID: <CA+V-a8vStea7RZWNXjJLbuibz+-53KT9=5g-P9N4fUrbqjj91A@mail.gmail.com>
Subject: Re: [RFC PATCH 1/4] regulator: core: Ensure the cached state matches
 the hardware state in regulator_set_voltage_unlocked()
To: Mark Brown <broonie@kernel.org>, Ulf Hansson <ulf.hansson@linaro.org>, 
	Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>, Rob Herring <robh@kernel.org>, 
	Krzysztof Kozlowski <krzk+dt@kernel.org>, Conor Dooley <conor+dt@kernel.org>, 
	Liam Girdwood <lgirdwood@gmail.com>, Magnus Damm <magnus.damm@gmail.com>, linux-mmc@vger.kernel.org, 
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-renesas-soc@vger.kernel.org, 
	Fabrizio Castro <fabrizio.castro.jz@renesas.com>, Biju Das <biju.das.jz@bp.renesas.com>, 
	Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
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Hi Mark,

On Thu, Jun 6, 2024 at 1:05=E2=80=AFPM Mark Brown <broonie@kernel.org> wrot=
e:
>
> On Wed, Jun 05, 2024 at 08:49:33AM +0100, Prabhakar wrote:
>
> > Driver code flow:
> > 1> set regulator to 1.8V (BIT0 =3D 1)
> > 2> Regulator cached state now will be 1.8V
> > 3> Now for some reason driver issues a reset to the IP block
> >    which resets the registers to default value. In this process
> >    the regulator is set to 3.3V (BIT0 =3D 0)
> > 4> Now the driver requests the regulator core to set 1.8V
>
> If something is resetting the regulator like this that's a problem in
> general, we need to either have the driver notify the core when that
> happens so it can reconfigure the regulator or have it reapply
> configuration directly.  Obviously it's not great to have that happen at
> all...
>
Currently I am seeing this problem with SDHI driver. For the voltage
switch operation the MMC core requests the driver to do the change and
similarly the MMC core requests the reset operation.

> Having the core driver notify the core when that happens so it can reconf=
igure the regulator or have it reapply configuration directly.
Again doing this would be a problem as MMC core also maintains the IOS
states, reconfiguring the regulator would cause conflicts between the
states.

Ulf/Wolfram - please correct me if I'm wrong here.

Cheers,
Prabhakar