linux-kernel - Re: [PATCH v1 1/2] dt-bindings: input: atmel,maxtouch: add poweroff-in-suspend property

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Message-ID: <ZXMV9gzFbc05IEKg@eichest-laptop>
Date:   Fri, 8 Dec 2023 14:11:18 +0100
From:   Stefan Eichenberger <eichest@...il.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     nick@...anahar.org, dmitry.torokhov@...il.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        nicolas.ferre@...rochip.com, alexandre.belloni@...tlin.com,
        claudiu.beznea@...on.dev, linux-input@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Stefan Eichenberger <stefan.eichenberger@...adex.com>
Subject: Re: [PATCH v1 1/2] dt-bindings: input: atmel,maxtouch: add
 poweroff-in-suspend property

Hi Krzysztof and Linux,

On Fri, Dec 08, 2023 at 01:54:21PM +0100, Linus Walleij wrote:
> On Thu, Dec 7, 2023 at 12:13 PM Stefan Eichenberger <eichest@...il.com> wrote:
> 
> > From: Stefan Eichenberger <stefan.eichenberger@...adex.com>
> >
> > Add a new property to indicate that the device should be powered off in
> > suspend mode.
> >
> > Signed-off-by: Stefan Eichenberger <stefan.eichenberger@...adex.com>
> (...)
> > +  atmel,poweroff-in-suspend:
> > +    description: |
> > +      When this property is set, all supplies are turned off when the system is
> > +      going to suspend.
> > +    type: boolean
>    wakeup-source:
>      type: boolean
> 
> As Krzysztof says it seems you are describing an operating system feature.
> 
> I can't help but wonder: shouldn't that pretty much be the default behaviour
> if wakeup-source is *not* specified?
> 
> I.e. the property kind of describes !wakeup-source.

The maxtouch controller has a deep sleep mode which is currently used
without powering down vdd and vdda. However, because we have a shared
regulator which powers other peripherals that we want to shut down in
suspend we need a way to power down vdd and vdda. However, I agree this
is not really a feature of the device. The feature would basically be
the internal deep sleep mode. I didn't want to change the default
behaviour of the driver, so I added this property but maybe I could
change it to:

atmel,deep-sleep:
  description: |
     Use the maxtouch deep-sleep mode instead of powering down vdd and
     vdda.

Or to not change the default behaviour:
atmel,no-deep-sleep:
  description: |
     Do not use the maxtouch deep-sleep mode but power down vdd and vdda
     in suspend.

As I understand the datasheet even if the maxtouch is using its deep
sleep mode it does not act as a wakeup source. It is just faster in
waking up because it can keep the configuration in memory.

Regards,
Stefan