Message-ID: <ivyujm6do2wmpgoa42amgli4yqthhqzme6xepzcj2ifzg7xzxp@rauwer3wjigp>
Date: Fri, 27 Sep 2024 11:35:25 +0200
From: Markus Schneider-Pargmann <msp@...libre.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Nishanth Menon <nm@...com>, Tero Kristo <kristo@...nel.org>, 
	Santosh Shilimkar <ssantosh@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Vignesh Raghavendra <vigneshr@...com>, Vibhore Vardhan <vibhore@...com>, 
	Kevin Hilman <khilman@...libre.com>, Dhruva Gole <d-gole@...com>, 
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/6] dt-bindings: ti, sci: Add property for
 partial-io-wakeup-sources

Hi Krzysztof,

On Thu, Sep 05, 2024 at 01:41:47PM GMT, Krzysztof Kozlowski wrote:
> On 05/09/2024 13:17, Markus Schneider-Pargmann wrote:
> > On Thu, Sep 05, 2024 at 12:41:05PM GMT, Krzysztof Kozlowski wrote:
> >> On 05/09/2024 11:49, Markus Schneider-Pargmann wrote:
> >>> On Thu, Sep 05, 2024 at 11:25:48AM GMT, Krzysztof Kozlowski wrote:
> >>>> On 05/09/2024 11:15, Krzysztof Kozlowski wrote:
> >>>>> On 05/09/2024 11:08, Markus Schneider-Pargmann wrote:
> >>>>>> On Tue, Aug 06, 2024 at 10:03:00AM GMT, Krzysztof Kozlowski wrote:
> >>>>>>> On 06/08/2024 09:11, Markus Schneider-Pargmann wrote:
> >>>>>>>> Hi Krzysztof,
> >>>>>>>>
> >>>>>>>> On Tue, Aug 06, 2024 at 08:18:01AM GMT, Krzysztof Kozlowski wrote:
> >>>>>>>>> On 29/07/2024 10:00, Markus Schneider-Pargmann wrote:
> >>>>>>>>>> Partial-IO is a very low power mode in which nearly everything is
> >>>>>>>>>> powered off. Only pins of a few hardware units are kept sensitive and
> >>>>>>>>>> are capable to wakeup the SoC. The device nodes are marked as
> >>>>>>>>>> 'wakeup-source' but so are a lot of other device nodes as well that are
> >>>>>>>>>> not able to do a wakeup from Partial-IO. This creates the need to
> >>>>>>>>>> describe the device nodes that are capable of wakeup from Partial-IO.
> >>>>>>>>>>
> >>>>>>>>>> This patch adds a property with a list of these nodes defining which
> >>>>>>>>>> devices can be used as wakeup sources in Partial-IO.
> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> <form letter>
> >>>>>>>>> This is a friendly reminder during the review process.
> >>>>>>>>>
> >>>>>>>>> It seems my or other reviewer's previous comments were not fully
> >>>>>>>>> addressed. Maybe the feedback got lost between the quotes, maybe you
> >>>>>>>>> just forgot to apply it. Please go back to the previous discussion and
> >>>>>>>>> either implement all requested changes or keep discussing them.
> >>>>>>>>>
> >>>>>>>>> Thank you.
> >>>>>>>>> </form letter>
> >>>>>>>>
> >>>>>>>> I tried to address your comment from last version by explaining more
> >>>>>>>> thoroughly what the binding is for as it seemed that my previous
> >>>>>>>> explanation wasn't really good.
> >>>>>>>>
> >>>>>>>> You are suggesting to use 'wakeup-source' exclusively. Unfortunately
> >>>>>>>> wakeup-source is a boolean property which covers two states. I have at
> >>>>>>>> least three states I need to describe:
> >>>>>>>>
> >>>>>>>>  - wakeup-source for suspend to memory and other low power modes
> >>>>>>>>  - wakeup-source for Partial-IO
> >>>>>>>>  - no wakeup-source
> >>>>>>>
> >>>>>>> Maybe we need generic property or maybe custom TI would be fine, but in
> >>>>>>> any case - whether device is wakeup and what sort of wakeup it is, is a
> >>>>>>> property of the device.
> >>>>>>
> >>>>>> To continue on this, I currently only know of this Partial-IO mode that
> >>>>>> would require a special flag like this. So I think a custom TI property
> >>>>>> would work. For example a bool property like
> >>>>>>
> >>>>>>   ti,partial-io-wakeup-source;
> >>>>>>
> >>>>>> in the device nodes for which it is relevant? This would be in addition
> >>>>>> to the 'wakeup-source' property.
> >>>>>
> >>>>> Rather oneOf. I don't think having two properties in a node brings any
> >>>>> more information.
> >>>>>
> >>>>> I would suggest finding one more user of this and making the
> >>>>> wakeup-source an enum - either string or integer with defines in a header.
> >>>>
> >>>> I am going through this thread again to write something in DT BoF but
> >>>> this is confusing:
> >>>>
> >>>> "Partial-IO is a very low power mode"
> >>>> "not able to do a wakeup from Partial-IO."
> >>>> "wakeup-source for Partial-IO"
> >>>>
> >>>> Are you waking up from Partial-IO or are you waking up into Partial-IO?
> >>>>
> >>>> And why the devices which are configured as wakeup-source cannot wake up
> >>>> from or for Partial-IO?
> >>>
> >>> Sorry if this is confusing. Let me try again.
> >>>
> >>> Partial-IO is a very low power mode. Only a small IO unit is switched on
> >>> to be sensitive on a small set of pins for any IO activity. The rest of
> >>> the SoC is powered off, including DDR. Any activity on these pins
> >>> switches on the power for the remaining SoC. This leads to a fresh boot,
> >>> not a resume of any kind. On am62 the pins that are sensitive and
> >>> therefore wakeup-source from this Partial-IO mode, are the pins of a few
> >>> CAN and UARTs from the MCU and Wkup section of the SoC.
> >>>
> >>> These CAN and UART wakeup-sources are also wakeup-sources for other low
> >>> power suspend to ram modes. But wakeup-sources for suspend to ram modes
> >>> are typically not a wakeup-source for Partial-IO as they are not powered
> >>> in Partial-IO.
> >>>
> >>> I hope this explains it better.
> >>
> >> Yeah, it's kind of obvious now that just use wakeup-source. Your
> >> hardware does not have two different methods of waking up. System is
> >> sleeping - either S2R or partial-IO or whatever - and you want it to be
> >> woken up.
> >>
> >> Entire property is unnecessary... and as I said before - you added it
> >> only for your driver. If same feedback is repeated and repeated, there
> >> is something in it...
> > 
> > It's not obvious for me. Maybe you can elaborate a bit.
> > 
> > The hardware has a different set of wakeup sources depending on the
> > power mode it is in and I would like to describe these different sets of
> > wakeup sources in the devicetree as for me this is a hardware property,
> > not a driver thing.
> 
> I stated the argument to which you did not respond: it will not matter
> for the device whether this is wakeup-source = S2R or wakeup-source =
> TI-Partial-IO or whatever.
> 
> Each device is or is not wakeup source.
> 
> And just because your device has some registers or some configuration
> does not mean this property is suitable for DT.

I came up with a different (better) way to model this in the devicetree.
This group of units that are powered in Partial-IO are all powered by
just one regulator that is always on. I can simply describe this in the
devicetree by defining the regulator and consumer relationship:

Defining the regulator as described in the board schematic:

  vddshv_canuart: regulator-7 {
         /* TPS22965DSGT */
         compatible = "regulator-fixed";
         regulator-name = "vddshv_canuart";
         regulator-min-microvolt = <3300000>;
         regulator-max-microvolt = <3300000>;
         vin-supply = <&vcc_3v3_main>;
         regulator-always-on;
         regulator-boot-on;
  };

Adding vio-supply to mcan and uarts, note, this binding does not exist
yet:

  &mcu_mcan0 {
         vio-supply = <&vddshv_canuart>;
  };

  &mcu_mcan1 {
         vio-supply = <&vddshv_canuart>;
  };

  &mcu_uart0 {
         vio-supply = <&vddshv_canuart>;
  };

  &wkup_uart0 {
         vio-supply = <&vddshv_canuart>;
  };

Best
Markus

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