linux-kernel - Re: [PATCH v3 2/9] ARM: dts: nspire: Use syscon-reboot to handle restart

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Date:   Thu, 27 Oct 2022 17:27:09 -0400
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Andrew Davis <afd@...com>, Lee Jones <lee@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Daniel Tang <dt.tangr@...il.com>,
        Fabian Vogt <fabian@...ter-vogt.de>
Cc:     devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/9] ARM: dts: nspire: Use syscon-reboot to handle
 restart

On 27/10/2022 17:07, Andrew Davis wrote:
> On 10/27/22 2:33 PM, Krzysztof Kozlowski wrote:
>> On 27/10/2022 14:13, Andrew Davis wrote:
>>> Writing this bit can be handled by the syscon-reboot driver.
>>> Add this node to DT.
>>>
>>> Signed-off-by: Andrew Davis <afd@...com>
>>> Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
>>> Tested-by: Fabian Vogt <fabian@...ter-vogt.de>
>>> Reviewed-by: Fabian Vogt <fabian@...ter-vogt.de>
>>> ---
>>>   arch/arm/boot/dts/nspire.dtsi | 7 +++++++
>>>   1 file changed, 7 insertions(+)
>>>
>>> diff --git a/arch/arm/boot/dts/nspire.dtsi b/arch/arm/boot/dts/nspire.dtsi
>>> index bb240e6a3a6f..48fbc9d533c3 100644
>>> --- a/arch/arm/boot/dts/nspire.dtsi
>>> +++ b/arch/arm/boot/dts/nspire.dtsi
>>> @@ -172,7 +172,14 @@ rtc: rtc@...90000 {
>>>   			};
>>>   
>>>   			misc: misc@...a0000 {
>>> +				compatible = "ti,nspire-misc", "syscon", "simple-mfd";
>>
>> You have syscon and simple-mfd, but bindings in patch #1 say only syscon.
>>
> 
> I'm not following, are you just saying my wording in the patch message just
> wasn't complete?

Your binding patch adds nspire compatible to the list of two items, so
you have two items in total - nspire followed by syscon.

What you implemented here is different.

> 
> Or are you saying something more about nodes that are both syscon and simple-mfd?
> In that case, having both syscon and simple-mfd seems rather common, looks like
> you added the rule for it[0].
> 
> Thinking on this, they almost represent the same thing. simple-mfd says "my child
> nodes should be considered devices", why do we need that? Couldn't we simply state
> that "syscon" node's children are always devices, I mean what else could they be,
> syscon is an MFD after all (and lives in drivers/mfd/).

No, syscon is not an MFD. Syscon means system controller and alone it
does not have children.

> 
> "syscon" often just says, others can use the registers within this node, so as a
> different option, make "syscon" a property of "simple-mfd" nodes. I'm seeing all
> these examples of devices that should have been children of the "syscon" device,
> but instead use
> 
> regmap = <&x>;
> syscon = <&x>;
> 
> or similar and put the device node out somewhere random. And in those cases,
> wouldn't it have been more correct to use the normal "reg" and "regions" to
> define the registers belonging to the child node/device?..

Sorry, I do not follow. How this is even related to your patch?

Your bindings say A, DTS say B. A != B. This needs fixing.

Unless you are asking me what your device is in general. This I don't
really know, but if you want to use it as regmap provider for system
registers and as a parent of syscon-based reboot device, then your
device is syscon and simple-mfd. With a specific compatible. Was this
your question?

Best regards,
Krzysztof