linux-kernel - Re: [PATCH v2 1/3] dt-bindings: power: reset: atmel,sama5d2-shdwc: add lpm binding

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Message-ID: <895aaf27-cfb7-4071-a62d-b9204c249cc1@microchip.com>
Date: Thu, 18 Sep 2025 08:44:45 -0700
From: Ryan Wanner <ryan.wanner@...rochip.com>
To: Conor Dooley <conor@...nel.org>
CC: <claudiu.beznea@...on.dev>, <sre@...nel.org>, <robh@...nel.org>,
	<krzk+dt@...nel.org>, <conor+dt@...nel.org>, <nicolas.ferre@...rochip.com>,
	<alexandre.belloni@...tlin.com>, <linux@...linux.org.uk>,
	<linux-pm@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
	Varshini Rajendran <varshini.rajendran@...rochip.com>
Subject: Re: [PATCH v2 1/3] dt-bindings: power: reset: atmel,sama5d2-shdwc:
 add lpm binding

On 9/17/25 12:38, Conor Dooley wrote:
> On Tue, Sep 16, 2025 at 12:50:30PM -0700, Ryan.Wanner@...rochip.com wrote:
>> From: Varshini Rajendran <varshini.rajendran@...rochip.com>
>>
>> Add microchip,lpm-connection binding which allows to specify the devices
>> the SHDWC's Low Power Mode pin is connected to.
>>
>> Signed-off-by: Varshini Rajendran <varshini.rajendran@...rochip.com>
>> [ryan.wanner@...rochip.com: Add sam9x7-shdwc SoC to properties check]
>> Signed-off-by: Ryan Wanner <Ryan.Wanner@...rochip.com>
>> ---
>>  .../power/reset/atmel,sama5d2-shdwc.yaml      | 19 +++++++++++++++++++
>>  1 file changed, 19 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/power/reset/atmel,sama5d2-shdwc.yaml b/Documentation/devicetree/bindings/power/reset/atmel,sama5d2-shdwc.yaml
>> index 9c34249b2d6d..668b541eb44c 100644
>> --- a/Documentation/devicetree/bindings/power/reset/atmel,sama5d2-shdwc.yaml
>> +++ b/Documentation/devicetree/bindings/power/reset/atmel,sama5d2-shdwc.yaml
>> @@ -56,6 +56,13 @@ properties:
>>      description: enable real-time timer wake-up
>>      type: boolean
>>  
>> +  microchip,lpm-connection:
>> +    description:
>> +      List of phandles to devices which are connected to SHDWC's Low Power Mode Pin.
>> +      The LPM pin is used to idicate to an external power supply or device to enter
>> +      or exit a special powering state.
>> +    $ref: /schemas/types.yaml#/definitions/phandle-array
> 
> This sounds like you're some kind of power-domain provider. Why doesn't
> that generic kind of thing work for you?

This is used by the MPUs shutdown controller to toggle external things
that need to be disabled.

In the case of the SAMA7G5EK board it is used to disable the 24MHz
oscillator and the 25MHz oscillator for the GMAC1 phy.

>From my understanding this is not a power-domain provider it is just
used to toggle devices to disable when the MPU is in a low power state
and to re-enable when the MPU is in a normal power state.

Ryan
> 
>> +
>>  patternProperties:
>>    "^input@[0-15]$":
>>      description:
>> @@ -96,6 +103,18 @@ allOf:
>>        properties:
>>          atmel,wakeup-rtt-timer: false
>>  
>> +  - if:
>> +      properties:
>> +        compatible:
>> +          contains:
>> +            enum:
>> +              - atmel,sama5d2-shdwc
>> +              - microchip,sam9x60-shdwc
>> +              - microchip,sam9x7-shdwc
>> +    then:
>> +      properties:
>> +        microchip,lpm-connection: false
>> +
>>  additionalProperties: false
>>  
>>  examples:
>> -- 
>> 2.43.0
>>