linux-kernel - Re: [PATCH v1 3/3] regulator: fixed: forward under-voltage events

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Message-ID: <ZSebeJKa0sEzNzP4@dc78bmyyyyyyyyyyyyydt-3.rev.dnainternet.fi>
Date:   Thu, 12 Oct 2023 10:08:40 +0300
From:   Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Oleksij Rempel <o.rempel@...gutronix.de>,
        Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        Naresh Solanki <naresh.solanki@...ements.com>,
        zev@...ilderbeest.net, Sebastian Reichel <sre@...nel.org>,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v1 3/3] regulator: fixed: forward under-voltage events

On Wed, Oct 11, 2023 at 12:38:19PM +0100, Mark Brown wrote:
> On Wed, Oct 11, 2023 at 09:59:31AM +0200, Oleksij Rempel wrote:
> 
> > Configuration through the device tree and kernel defaults is preferable.
> > For instance, having a default kernel governor that doesn’t require user
> > space configuration aligns with the project’s objectives.
> 
> That's policy though...
> 
> > 
> > > For the regulator itself we probably want a way to identify regulators
> > > as being system critical so they start notifying.  It would be tempting

Can the "criticality" could be determined by the severity (ERROR vs WARNING)?

> > > to just do that by default but that would likely cause some issues for
> > > example with regulators for things like SD cards which are more likely
> > > to get hardware problems that don't comprimise the entire system.  We

"comprimise the entire system" sounds (to my ears) exactly the
difference between WARNING and ERROR notifications.

> > > could do that with DT, either a property or some sort of runtime
> > > consumer, but it might be better to have a control in sysfs that
> > > userspace can turn on?  OTOH the ability do something about this depends
> > > on specific hardware design...
> > > 
> > > I've copied in Sebastian since this sounds like the sort of thing that
> > > power supplies might have some kind of handling for, or at least if we
> > > need to add something we should make it so that the power supplies can
> > > be joined up to it.  I do see temperature and capacity alerts in the
> > > sysfs ABI for power supplies, but nothing for voltage.
> > 
> > Thank you for pointing towards the power supply framework. Given the hardware
> > design of my project, I can envision mapping the following states and
> > properties within this framework:
> 
> There's also hw_failure_emergency_poweroff() which looks like exactly
> what you're trying to trigger here.

There is already a path from regulator notification handling to the
hw_failure_emergency_poweroff() - although only when handling the IRQs
fail and this failure is marked as fatal.

> > Considering the above mapping, my initial step would be to create a simple
> > regulator coupled (if regulator is still needed in this casr) with a Device
> > Tree (DT) based power supply driver.  This setup would align with the existing
> > power supply framework, with a notable extension being the system-wide
> > notification for emergency shutdown upon under-voltage detection.
> 
> It sounds like this is actually a regulator regardless of if it also
> appears via some other API.

I wonder if it would make sense to add a 'protector' in regulator core.
The 'protector' could register to listen the notifications from those
regulators which have some
'regulator-fatal-notifications = <list of notifications>;' -property
defined in device-tree.

In my eyes the device-tree is correct place for this information
because whether an "anomaly" in regulator output compromises the system
is a property of hardware.

Yours,
	-- Matti

-- 
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =] 

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