linux-kernel - Re: [PATCH 1/4] dt-bindings: reset: add generic bit reset controller

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Message-ID: <bzzwckg2ac2q4fkcp5jju5ubqmget3jdwmvcubdmc4xp3slmwn@hn4kmkotfnfw>
Date: Thu, 13 Feb 2025 19:26:15 +0800
From: Inochi Amaoto <inochiama@...il.com>
To: Philipp Zabel <p.zabel@...gutronix.de>, 
	Inochi Amaoto <inochiama@...il.com>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Chen Wang <unicorn_wang@...look.com>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, Guo Ren <guoren@...nel.org>, 
	Uwe Kleine-König <u.kleine-koenig@...libre.com>
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	sophgo@...ts.linux.dev, linux-riscv@...ts.infradead.org, Yixun Lan <dlan@...too.org>, 
	Longbin Li <looong.bin@...il.com>
Subject: Re: [PATCH 1/4] dt-bindings: reset: add generic bit reset controller

On Thu, Feb 13, 2025 at 11:08:59AM +0100, Philipp Zabel wrote:
> On Do, 2025-02-13 at 10:08 +0800, Inochi Amaoto wrote:
> > Some SoCs from Aspeed, Allwinner, Sophgo and Synopsys have
> > a simple reset controller by toggling bit. It is a hard time
> > for each device to add its own compatible to the driver.
> > Since this device share a common design, it is possible to
> > add a common device to reduce these unnecessary change.
> > 
> > Add common binding for these kind generic reset controller.
> > 
> > Signed-off-by: Inochi Amaoto <inochiama@...il.com>
> > ---
> >  .../bindings/reset/reset-simple.yaml          | 42 +++++++++++++++++++
> >  1 file changed, 42 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/reset/reset-simple.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/reset/reset-simple.yaml b/Documentation/devicetree/bindings/reset/reset-simple.yaml
> > new file mode 100644
> > index 000000000000..77584e23e8e8
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/reset/reset-simple.yaml
> > @@ -0,0 +1,42 @@
> > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/reset/reset-simple.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Generic BIT Reset Controller
> > +
> > +maintainers:
> > +  - Inochi Amaoto <inochiama@...il.com>
> > +
> > +description:
> > +  Some reset controller devices uses a simple method to perform
> > +  assert/deassert by toggling bit. Some SoCs from Aspeed, Allwinner,
> > +  Sophgo and Synopsys have this kind of reset controller instances.
> 
> I think some properties should be documented that make reset
> controllers "simple" according to this binding.
> 
> For example, right now, the reset-simple driver assumes the following:
> 
>   - There is a single, contiguous range of 32-bit registers.
>   - All bits in each register directly control a reset line.
>      - There are no self-deasserting resets.
>      - There are no timing requirements.
>      - The bits are exclusively resets, nothing else.
>   - All bits behave the same, so all reset bits are either
>     active-high or all are active-low.
>   - The bits can be read back, but the read status may
>     be active-low independently from the writes.
> 

Thanks, I will add these assumes in to the binding.

> > +properties:
> > +  compatible:
> > +    enum:
> > +      - reset-simple-high
> > +      - reset-simple-low
> 
> I wonder if it would be better to have a single
> 
>   compatible:
>     const: reset-simple
> 
> and a boolean property, e.g.
> 
>   active-low:
>     type: boolean
> 
> like in leds/common.yaml. Also it should be documented clearly what
> this means for reads and writes.
> 

Yeah, it is better to have a property instead of defining a base
compatible. With this property, there are two ways to process this
property with existing device:

1. If device has defined the data, the active-low is ignored
2. If device has defined the data, the active-low will overwrite
   the device data.

I wonder which one is better?

> > +  reg:
> > +    maxItems: 1
> > +
> > +  "#reset-cells":
> > +    const: 1
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - "#reset-cells"
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    reset-controller@...0000 {
> > +        compatible = "reset-simple-high";
> 
> The example should probably include a SoC specific compatible?
> 
> regards
> Philipp

I think it is OK. But I think it should be added when a
specific compatible is coming.

Regards,
Inochi