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

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Message-ID: <ZXMwzqF8tHZuWVBN@eichest-laptop>
Date:   Fri, 8 Dec 2023 16:05:50 +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 Linus,

On Fri, Dec 08, 2023 at 03:23:54PM +0100, Linus Walleij wrote:
> On Fri, Dec 8, 2023 at 2:11 PM Stefan Eichenberger <eichest@...il.com> wrote:
> 
> > > 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.
> 
> While it is of no concern to the device tree bindings, Linux regulators
> are counting meaning that you need to make all peripherals disable
> their regulators and it will come down.

Yes we are working on that one. This is the last driver we need to allow
disabling the regulator, afterward it should hoepfully work on our
target system.

> 
> > 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.
> 
> Do you mean it can still work as a wakeup source in deep sleep mode?
> (there is a "not" too much above ...)

Sorry for the confusion. As it is configured now, it can not work as
wakeup source in deep sleep mode. Touch is completely disabled.

> > It is just faster in
> > waking up because it can keep the configuration in memory.
> 
> That sounds like a good reason to have the property, because that
> means that if you can control the wakeup latency and specify in the binding
> how much in absolute time units it is affected.
> 
> I would define it in positive terms instead of reverse "no-deep-sleep"
> though such as "atmel,fast-wakeup".
> 
> And: If you disable the regulators it will probably *not* be able to wake the
> system up, right? And that is just a few lines of code in the driver such as:
> 
> go_to_sleep():
>   if (!wakeup_source):
>      disable_regulators()

So to not change the default behaviour I would have to name it:
atmel,slow-wakeup
or maybe even full wakeup because it does a wakeup from the disabled
state?
atmel,full-wakeup

Exactly, the added code looks more or less exactly as you wrote. And on
resume it does the opposite + configure it:

resume():
  if (!wakeup_source):
     enable_regulators()
     configure_maxtouch()

Regards,
Stefan