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

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Date: Thu, 27 Jun 2024 14:44:05 -0600
From: Rob Herring <robh@...nel.org>
To: Jiaxun Yang <jiaxun.yang@...goat.com>
Cc: Krzysztof Kozlowski <krzk@...nel.org>, Lee Jones <lee@...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>,
	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 Wed, Jun 19, 2024 at 12:20:54PM +0100, Jiaxun Yang wrote:
> 
> 
> 在2024年6月19日六月 上午10:28，Krzysztof Kozlowski写道：
> > On 18/06/2024 17:11, Jiaxun Yang wrote:
> >> This compatible has been used in arch/mips/boot/dts/img/boston.dts
> >> for a while but never documented properly.
> >> 
> >
> >> diff --git a/Documentation/devicetree/bindings/mfd/img,boston-platform-regs.yaml b/Documentation/devicetree/bindings/mfd/img,boston-platform-regs.yaml
> >> new file mode 100644
> >> index 000000000000..79cae87c6758
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/mfd/img,boston-platform-regs.yaml
> >> @@ -0,0 +1,74 @@
> >> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> >> +%YAML 1.2
> >> +---
> >> +$id: http://devicetree.org/schemas/mfd/img,boston-platform-regs.yaml#
> >> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> >> +
> >> +title: Imagination Technologies Boston Platform Registers
> >> +
> >> +maintainers:
> >> +  - Jiaxun Yang <jiaxun.yang@...goat.com>
> >> +
> >> +properties:
> >> +  compatible:
> >> +    items:
> >> +      - const: img,boston-platform-regs
> >> +      - const: syscon
> >> +      - const: simple-mfd
> >
> >
> > Fix U-boot to populate devices instead of relying on simple-mfd.
> 
> 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.
> 
> Linux managed to work without "simple-mfd" only because clock subsystem
> is bypassing regular OF population process. Semantically we need this.

I'm confused. Neither u-boot nor linux .dts files have 'simple-mfd' for 
this binding. So why do you need it? Why are we changing a platform 
that's had 1 dts change since 2018?

If anything, add it in a separate patch and we can discuss it there 
instead of a conversion.

> Besides Linux as upstream of devicetree source had accepted U-Boot
> only stuff here, such as "bootph-all" property.

Yes, and there are things we've rejected. See Arm FFA threads if you 
want to waste a few hours reading.

Rob