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

From: Ahmad Fatoum
Date: Mon Oct 26 2020 - 17:30:22 EST


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@xxxxxxxxxxxxxx>
>> ---
>> v1 available here:
>> https://lore.kernel.org/linux-arm-kernel/20200916142216.25142-1-a.fatoum@xxxxxxxxxxxxxx/
>>
>> v1 -> v2:
>> - new patch, rebased on top of
>> https://lore.kernel.org/r/20201014125441.2457-1-arnaud.pouliquen@xxxxxx
>> ---
>> .../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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