linux-kernel - Re: Where to update regulator register with initial voltage set by HW

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Date:   Tue, 4 Jul 2017 12:58:04 +0200
From:   Waldemar Rymarkiewicz <waldemar.rymarkiewicz@...il.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     "Bartholomae, Thomas" <t.bartholomae@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Liam Girdwood <lgirdwood@...il.com>
Subject: Re: Where to update regulator register with initial voltage set by HW

Hi Mark,

On 3 July 2017 at 17:36, Mark Brown <broonie@...nel.org> wrote:
> On Mon, Jul 03, 2017 at 05:33:03PM +0200, Waldemar Rymarkiewicz wrote:
>
>> I've asked also on TI forum if this is typical to the regulator not to
>> determine the startup voltage but still waiting for feedback. Anyway,
>> if this is the case I guess a driver is a good place to update
>> register before we register to the regulator framework.
>
> It's really unusual to have a device that has the voltage changable by
> register write at runtime where the current state can't be read back.

or you did not realise that this is initialised by bootloader for example.

After investigating this issue a bit more I've found that this is
rather typical for power regulators not to update a register with
startup voltage set by a feedback resistor divider as it would cost
extra circuit.  So, I assume that most likely a bootloader normally
initializes power regulator in case it's needed eg. if it's supplying
CPU which is DVS-enabled.

Anyway, it's more clear now to me how this should be done.

/Waldek