linux-kernel - Re: [PATCH v4 2/4] dt-bindings: soc: spacemit: Add spacemit,k1-syscon

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Message-ID: <19e5129b-8423-4660-8e4f-8b898214d275@kernel.org>
Date: Tue, 11 Feb 2025 09:03:20 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Haylen Chu <heylenay@....org>
Cc: Michael Turquette <mturquette@...libre.com>,
 Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Haylen Chu <heylenay@...look.com>,
 Yixun Lan <dlan@...too.org>, linux-riscv@...ts.infradead.org,
 linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, Inochi Amaoto <inochiama@...look.com>,
 Chen Wang <unicornxdotw@...mail.com>, Jisheng Zhang <jszhang@...nel.org>,
 Meng Zhang <zhangmeng.kevin@...ux.spacemit.com>
Subject: Re: [PATCH v4 2/4] dt-bindings: soc: spacemit: Add spacemit,k1-syscon

On 11/02/2025 06:15, Haylen Chu wrote:
> On Sat, Jan 04, 2025 at 11:07:58AM +0100, Krzysztof Kozlowski wrote:
>> On Fri, Jan 03, 2025 at 09:56:35PM +0000, Haylen Chu wrote:
>>> Add documentation to describe Spacemit K1 system controller registers.
>>>
>>> Signed-off-by: Haylen Chu <heylenay@....org>
>>> ---
>>>  .../soc/spacemit/spacemit,k1-syscon.yaml      | 52 +++++++++++++++++++
>>>  1 file changed, 52 insertions(+)
>>>  create mode 100644 Documentation/devicetree/bindings/soc/spacemit/spacemit,k1-syscon.yaml
>>>
>>> diff --git a/Documentation/devicetree/bindings/soc/spacemit/spacemit,k1-syscon.yaml b/Documentation/devicetree/bindings/soc/spacemit/spacemit,k1-syscon.yaml
>>> new file mode 100644
>>> index 000000000000..79c4a74ff30e
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/soc/spacemit/spacemit,k1-syscon.yaml
>>> @@ -0,0 +1,52 @@
>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>> +%YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/soc/spacemit/spacemit,k1-syscon.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: Spacemit K1 SoC System Controller
>>> +
>>> +maintainers:
>>> +  - Haylen Chu <heylenay@....org>
>>> +
>>> +description:
>>> +  The Spacemit K1 SoC system controller provides access to shared register files
>>> +  for related SoC modules, such as clock controller and reset controller.
>>> +
>>> +properties:
>>> +  compatible:
>>> +    items:
>>> +      - enum:
>>> +          - spacemit,k1-apbc-syscon
>>> +          - spacemit,k1-apbs-syscon
>>> +          - spacemit,k1-apmu-syscon
>>> +          - spacemit,k1-mpmu-syscon
>>> +      - const: syscon
>>> +      - const: simple-mfd
>>> +
>>> +  reg:
>>> +    maxItems: 1
>>> +
>>> +  clock-controller:
>>> +    $ref: /schemas/clock/spacemit,k1-ccu.yaml#
>>> +    type: object
>>
>> So now we see the full picture and it leads to questions.
>>
>> 1. Why spacemit,k1-apbc-syscon with spacemit,k1-ccu-apmu child is a
>> correct combination?
>>
>> 2. Why having this split in the first place? Please confirm that clock
>> controller is really, really a separate device and its child in
>> datasheet. IOW, fake child for your Linux is a no-go. Fake child while
>> devices are independent is another no-go.
> 
> These syscons are introduced because the clock controllers share
> registers with reset controllers. Folding them into the parents results

So a fake split...

> in devicetree nodes act as both reset and clock controllers, like what

Which is correct hardware representation, isn't it?

> has been done for Rockchip SoCs. Such folding isn't practical for the
> MPMU region either, since watchdog and other misc bits (e.g. PLL lock
> status) locates in it.

Hm? Why? You have a device which is reset and clock controller, so why
one device node is not practical? Other vendors do not have problem with
this.

> 
> If you're more comfortable with reset and clock controllers folded
> together and eliminating most of these syscons, I'm willing to make the
> change.

This is expected.



Best regards,
Krzysztof