linux-kernel - Re: [PATCH RFC] regulator: core: fix handling negative voltages e.g. in EPD PMICs

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Message-Id: <1548203B-9D64-4128-9BED-D3BC30F9DC49@goldelico.com>
Date:   Mon, 24 Feb 2020 13:22:21 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Andreas Kemnade <andreas@...nade.info>, j.neuschaefer@....net,
        contact@...lk.fr, GNUtoo@...erdimension.org, josua.mayer@....eu,
        lgirdwood@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] regulator: core: fix handling negative voltages e.g. in EPD PMICs

> Am 24.02.2020 um 13:05 schrieb Mark Brown <broonie@...nel.org>:
> 
> On Sun, Feb 23, 2020 at 04:35:01PM +0100, Andreas Kemnade wrote:
> 
>> An alternative would be to handle voltages as absolute values.
>> There are probably no regulators with support both negative
>> and positive output.
> 
> This is what'd be needed, your approach here is a bit of a hack and
> leaves some values unrepresentable if they overlap with errnos which
> obviously has issues if someone has a need for those values.

Negative ERRNOs have BIT(31) set.

Since voltage integers on a 32 bit architecture represent µV this would
still allow voltages up to (2^31 - 1) µV i.e. 2 kV with BIT(31) not set.

Therefore it seems very unlikely that anyone needs to represent voltages
above 2 kV within a Linux system through a regulator.

So I'd say any negative return value got regulator_get_voltage() can be
treated as an error.

And regulators for negative voltages could be represented by
their absolute value (and maybe a _neg component in the regulator
name).

But then it seems to be a little inconsistent that the voltage
parameters of regulator_set_voltage_unlocked() are signed integers
and not unsigned.

So shouldn't that be protected against attempting to set negative voltages?

Just my 2 cts.

BR,
Nikolaus