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Date:   Tue, 10 Oct 2023 15:39:35 +0200
From:   Oleksij Rempel <o.rempel@pengutronix.de>
To:     Mark Brown <broonie@kernel.org>
Cc:     Liam Girdwood <lgirdwood@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>, kernel@pengutronix.de,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org
Subject: Re: [PATCH v1 3/3] regulator: fixed: forward under-voltage events
Message-ID: <20231010133935.GB3268051@pengutronix.de>
References: <20231010085906.3440452-1-o.rempel@pengutronix.de>
 <20231010085906.3440452-3-o.rempel@pengutronix.de>
 <5e51792a-cc93-4364-a51b-c2b116d89369@sirena.org.uk>
 <20231010125531.GA3268051@pengutronix.de>
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On Tue, Oct 10, 2023 at 02:55:31PM +0200, Oleksij Rempel wrote:
> Hi,
> 
> On Tue, Oct 10, 2023 at 01:19:36PM +0100, Mark Brown wrote:
> > On Tue, Oct 10, 2023 at 10:59:06AM +0200, Oleksij Rempel wrote:
> > > Add handler to forward under-voltage events.
> > > On systems for more or less complicated regulator chains we need to
> > > forward under-voltage events to actual driver which need to react on
> > > them.
> > 
> > It isn't clear to me why this would be implemented in one specific
> > driver, nor why this would be done unconditionally.  Could you provide
> > some information on the problem you're trying to solve here?
> 
> The hardware I am working with has an under-voltage sensor on the 24V
> supply regulator and some backup capacitors to run SoC for 100ms. I want
> to forward under-voltage events across a chain of different regulators
> to a designated consumer. For instance, to the mmc driver, enabling it
> to initiate shutdown before power loss occurs.  Additionally, a bit can
> be set in the volatile memory of a scratch pad in an RTC clock to record
> sudden power loss, which can be checked on the next system start.

The bit picture of my HW may potentially be even more advanced:
- some regulator chain paths are disabled by the HW. With other words
  under-voltage event is converted to fail or disable. There is nothing
  what software can do, but it will be good to reflect it on the SW
  side for diagnostic.
- some paths can be disabled by software to get some more milliseconds
  of life and complete emergency shutdown task.


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