Message-ID: <58f5f778-9f0a-4a05-8c33-949f3b3d1f49@kernel.org>
Date: Thu, 5 Sep 2024 12:41:05 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Markus Schneider-Pargmann <msp@...libre.com>
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 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...

Best regards,
Krzysztof

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