linux-kernel - Re: [PATCH v2 1/2] dt-bindings: arm: stm32: add simple-mfd compatible for tamp node

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Date:   Mon, 26 Oct 2020 22:30:17 +0100
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     Rob Herring <robh@...nel.org>
Cc:     Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Christophe Roullier <christophe.roullier@...com>,
        kernel@...gutronix.de, Arnaud Pouliquen <arnaud.pouliquen@...com>,
        devicetree@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] dt-bindings: arm: stm32: add simple-mfd compatible
 for tamp node

Hello Rob,

On 10/26/20 3:36 PM, Rob Herring wrote:
> On Wed, Oct 21, 2020 at 12:28:55PM +0200, Ahmad Fatoum wrote:
>> The stm32mp1 TAMP (Tamper and backup registers) does tamper detection
>> and features 32 backup registers that, being in the RTC domain, may
>> survive even with Vdd switched off.
>>
>> This makes it suitable for use to communicate a reboot mode from OS
>> to bootloader via the syscon-reboot-mode binding. Add a "simple-mfd"
>> to support probing such a child node. The actual reboot mode
>> node could then be defined in a board.dts or fixed up by the bootloader.
> 
> 'simple-mfd' implies there is no dependency on the parent node for the 
> child (such as the regmap perhaps). Is that the case here?

No, there's a dependency and the Linux driver does syscon_node_to_regmap
on the device tree node's parent but that's how the syscon-reboot-mode binding
is documented:

  The SYSCON mapped register is retrieved from the
  parental dt-node plus the offset. So the SYSCON reboot-mode node
  should be represented as a sub-node of a "syscon", "simple-mfd" node.

How would you prefer this being done instead?

Cheers,
Ahmad

> 
>>
>> Signed-off-by: Ahmad Fatoum <a.fatoum@...gutronix.de>
>> ---
>> v1 available here:
>> https://lore.kernel.org/linux-arm-kernel/20200916142216.25142-1-a.fatoum@pengutronix.de/
>>
>> v1 -> v2:
>>  - new patch, rebased on top of
>>    https://lore.kernel.org/r/20201014125441.2457-1-arnaud.pouliquen@st.com
>> ---
>>  .../devicetree/bindings/arm/stm32/st,stm32-syscon.yaml       | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/devicetree/bindings/arm/stm32/st,stm32-syscon.yaml b/Documentation/devicetree/bindings/arm/stm32/st,stm32-syscon.yaml
>> index 6634b3e0853e..4684017a42e4 100644
>> --- a/Documentation/devicetree/bindings/arm/stm32/st,stm32-syscon.yaml
>> +++ b/Documentation/devicetree/bindings/arm/stm32/st,stm32-syscon.yaml
>> @@ -19,8 +19,11 @@ properties:
>>                - st,stm32mp151-pwr-mcu
>>                - st,stm32-syscfg
>>                - st,stm32-power-config
>> -              - st,stm32-tamp
>>            - const: syscon
>> +      - items:
>> +          - const: st,stm32-tamp
>> +          - const: syscon
>> +          - const: simple-mfd
>>  
>>    reg:
>>      maxItems: 1
>> -- 
>> 2.28.0
>>
> 

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