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Date:   Tue, 10 Oct 2023 14:55:31 +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: <20231010125531.GA3268051@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>
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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.

> This feels like something that should be a core feature.

Agreed. I am relatively new to the regulator framework and am uncertain
about the optimal location for registering the event forwarding. Could
you advise on this?

> > +static int reg_fixed_regulator_notifier(struct notifier_block *nb,
> > +					unsigned long event, void *data)
> > +{
> > +	struct fixed_voltage_data *priv =
> > +		container_of(nb, struct fixed_voltage_data, nb);
> > +	struct regulator_dev *rdev = priv->dev;
> > +
> > +	if (event != REGULATOR_EVENT_UNDER_VOLTAGE_WARN &&
> > +	    event != REGULATOR_EVENT_UNDER_VOLTAGE)
> > +		return NOTIFY_OK;
> > +
> > +	regulator_notifier_call_chain(rdev, event, NULL);
> 
> This would be better written as a switch statement for extensibility,

ack.

> and it's not clear why the filtering?

I started with a conservative approach because I'm not sure about the
possible effects of forwarding all events. If forwarding all events is a
good idea, I can do it.

Regards,
Oleksij
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