linux-kernel - Re: [PATCH v10 02/10] dt-bindings: power: reset: Document reboot-mode cookie

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Message-ID: <cdadd6cf-18c9-15c7-c58a-b5d56b53452a@oss.qualcomm.com>
Date: Fri, 11 Jul 2025 18:02:15 +0530
From: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
To: Rob Herring <robh@...nel.org>
Cc: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
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 <conor+dt@...nel.org>,
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Subject: Re: [PATCH v10 02/10] dt-bindings: power: reset: Document reboot-mode
 cookie



On 7/11/2025 4:17 AM, Rob Herring wrote:
> On Thu, Jul 10, 2025 at 02:45:44PM +0530, Shivendra Pratap wrote:
>> Update the reboot-mode binding to support an optional cookie
>> value in mode-<cmd> properties. The cookie is used to supply
>> additional data for reboot modes that accept two arguments.
>>
>> Signed-off-by: Shivendra Pratap <shivendra.pratap@....qualcomm.com>
>> ---
>>  .../devicetree/bindings/power/reset/reboot-mode.yaml         | 12 +++++++-----
>>  1 file changed, 7 insertions(+), 5 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/power/reset/reboot-mode.yaml b/Documentation/devicetree/bindings/power/reset/reboot-mode.yaml
>> index 3ddac06cec7277789b066d8426ea77d293298fac..a4d2fe1db51e0c1f34ebefddaad82b8cc0b1b34a 100644
>> --- a/Documentation/devicetree/bindings/power/reset/reboot-mode.yaml
>> +++ b/Documentation/devicetree/bindings/power/reset/reboot-mode.yaml
>> @@ -10,14 +10,15 @@ maintainers:
>>    - Andy Yan <andy.yan@...k-chips.com>
>>  
>>  description: |
>> -  This driver get reboot mode arguments and call the write
>> -  interface to store the magic value in special register
>> -  or ram. Then the bootloader can read it and take different
>> -  action according to the argument stored.
>> +  This driver gets reboot mode arguments and calls the write
>> +  interface to store the magic and an optional cookie value
>> +  in special register or ram. Then the bootloader can read it
>> +  and take different action according to the argument stored.
>>  
>>    All mode properties are vendor specific, it is a indication to tell
>>    the bootloader what to do when the system reboots, and should be named
>> -  as mode-xxx = <magic> (xxx is mode name, magic should be a non-zero value).
>> +  as mode-xxx = <magic cookie> (xxx is mode name, magic should be a
>> +  non-zero value, cookie is optional).
> 
> I don't understand the distinction between magic and cookie... Isn't all 
> just magic values and some platform needs more than 32-bits of it?
Need two different arguments. Will try to clarify a bit below.
PSCI defines SYSTEM_RESET2 vendor-specific resets which takes two
parameters - reset_type and cookie. Both parameters are independent and
used by firmware to define different types of resets or shutdown.
As per spec:
reset_type: Values in the range 0x80000000-0xFFFFFFFF of the reset_type parameter
can be used to request vendor-specific resets or shutdowns.
cookie: the cookie parameter can be used to pass additional data to the 
implementation.

Now to implement SYSTEM_RESET2 vendor-specific resets using reboot-mode
driver, we will need two separate arguments. reboot-mode already defines a
magic, which will be used as reset_type. For the second parameter requirement of
SYSTEM_RESET2, we add support for additional argument cookie.
> 
>>  
>>    For example, modes common Android platform are:
>>      - normal: Normal reboot mode, system reboot with command "reboot".
>> @@ -45,5 +46,6 @@ examples:
>>        mode-recovery = <1>;
>>        mode-bootloader = <2>;
>>        mode-loader = <3>;
>> +      mode-edl = <1 2>;
>>      };
>>  ...
>>
>> -- 
>> 2.34.1
>>