linux-kernel - Re: [PATCH v3 7/8] dt-bindings: mfd: Add img,boston-platform-regs

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Message-ID: <6ca74ccf-b93e-4d77-8609-a12a96c15f38@kernel.org>
Date: Sat, 22 Jun 2024 20:12:17 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Jiaxun Yang <jiaxun.yang@...goat.com>, Lee Jones <lee@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>,
 "paulburton@...nel.org" <paulburton@...nel.org>,
 Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>
Subject: Re: [PATCH v3 7/8] dt-bindings: mfd: Add img,boston-platform-regs

On 21/06/2024 17:51, Jiaxun Yang wrote:
> 
> 
> 在2024年6月20日六月 上午7:40，Krzysztof Kozlowski写道：
> [...]
>>>
>>> Hi Krzysztof,
>>>
>>> I believe U-Boot's implementation is correct. As per simple-mfd binding:
>>>
>>> ```
>>> simple-mfd" - this signifies that the operating system should
>>>   consider all subnodes of the MFD device as separate devices akin to how
>>>   "simple-bus" indicates when to see subnodes as children for a simple
>>>   memory-mapped bus.
>>> ```
>>>
>>> This reads to me as "if you want sub nodes to be populated as devices
>>> you need this."
>>>
>>> In our case there are "clock" and "reset" node sub nodes which should be
>>> probed as regular device, so it's true for us.
>>
>> No, you already got comment from Rob.
>>
>> Your children depend on parent to provide IO address, so this is not
>> simple-mfd. Rule for simple-mfd is that children do not rely on parent
>> at all.
>>
> Hi Krzysztof,
> 
> Sorry but can I ask for clarification on "depend on parent to provide IO
> address", do you mind explaining it a little bit? Does it mean children
> should get regmap node from a phandle property, not the parent node? Or there
> should be a reg property for child node to tell register offset etc?
> 
> There are way too much usage that children "depends" on parents somehow
> in tree, so I want to confirm my understanding.


Your driver relies on parent IO address to be provided - what's more to
explain here? If parent does not provide syscon, does the child work?
No. Therefore it is not suited for simple-mfd.

> 
> For boston-platform-regs there are some other PHYs that I may add drivers
> for them in future, so I certainly want "simple-mfd" to be here 

Well, I want a new Ducati, but we don't always get what we want, right?

Best regards,
Krzysztof