Message-ID: <sisw3whyzr7itjtuznvt5t6cbmfxzop5c4nfrxwpxjil6rxqzc@cfnb5panavxe>
Date: Thu, 5 Sep 2024 13:17:45 +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

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.

Best
Markus

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