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

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Date:   Tue, 10 Nov 2020 11:27:57 +0100
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     Alexandre Torgue <alexandre.torgue@...com>
Cc:     Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Christophe Roullier <christophe.roullier@...com>,
        Sascha Hauer <kernel@...gutronix.de>,
        Arnaud Pouliquen <arnaud.pouliquen@...com>,
        devicetree@...r.kernel.org,
        "moderated list:ARM/STM32 ARCHITECTURE" 
        <linux-stm32@...md-mailman.stormreply.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v2 1/2] dt-bindings: arm: stm32: add simple-mfd compatible
 for tamp node

Hello Alex,

On 10/27/20 1:15 PM, Rob Herring wrote:
> On Mon, Oct 26, 2020 at 4:30 PM Ahmad Fatoum <a.fatoum@...gutronix.de> wrote:
>>
>> 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?
> 
> Well, probably the syscon driver could just probe any children, but
> I'm not sure if that would break anyone. So I guess fine as-is.
> 
> Reviewed-by: Rob Herring <robh@...nel.org>

Gentle ping.

> 
> Rob
> 

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