linux-kernel - Re: [PATCH v4 2/4] dt-bindings: soc: spacemit: Add K1 MBUS controller

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Message-ID: <20250527-energetic-pink-cricket-a282fd@kuoka>
Date: Tue, 27 May 2025 08:51:19 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Ze Huang <huangze@...t.edu.cn>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Yixun Lan <dlan@...too.org>, 
	Thinh Nguyen <Thinh.Nguyen@...opsys.com>, Philipp Zabel <p.zabel@...gutronix.de>, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>, linux-usb@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-riscv@...ts.infradead.org, spacemit@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/4] dt-bindings: soc: spacemit: Add K1 MBUS controller

On Mon, May 26, 2025 at 10:40:18PM GMT, Ze Huang wrote:
> Some devices on the SpacemiT K1 SoC perform DMA through a memory bus
> (MBUS) that is not their immediate parent in the device tree. This bus
> uses a different address mapping than the CPU.
> 
> To express this topology properly, devices are expected to use the
> interconnects with name "dma-mem" to reference the MBUS controller.

I don't get it, sorry. Devices performing DMA through foo-bar should use
dmas property for foo-bar DMA controller. Interconnects is not for that.


> 
> Signed-off-by: Ze Huang <huangze@...t.edu.cn>
> ---
>  .../bindings/soc/spacemit/spacemit,k1-mbus.yaml    | 55 ++++++++++++++++++++++
>  1 file changed, 55 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/soc/spacemit/spacemit,k1-mbus.yaml b/Documentation/devicetree/bindings/soc/spacemit/spacemit,k1-mbus.yaml
> new file mode 100644
> index 0000000000000000000000000000000000000000..533cf99dff689cf55a159118c32a676054294ffa
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/soc/spacemit/spacemit,k1-mbus.yaml
> @@ -0,0 +1,55 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/soc/spacemit/spacemit,k1-mbus.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: SpacemiT Memory Bus controller
> +
> +maintainers:
> +  - Ze Huang <huangze9015@...il.com>
> +
> +description: |
> +  On the SpacemiT K1 SoC, some devices do not perform DMA through their
> +  immediate parent node in the device tree. Instead, they access memory
> +  through a separate memory bus (MBUS) that uses a different address
> +  mapping from the CPU.
> +
> +  To correctly describe the DMA path, such devices must reference the MBUS
> +  controller through an interconnect with the reserved name "dma-mem".
> +
> +properties:
> +  compatible:
> +    const: spacemit,k1-mbus
> +
> +  reg:
> +    maxItems: 1
> +
> +  dma-ranges:
> +    maxItems: 1
> +
> +  "#address-cells": true
> +
> +  "#size-cells": true

No improvements.


> +
> +  "#interconnect-cells":
> +    const: 0

This is not a interconnect provider, but DMA controller, according to
youro description.

> +
> +required:
> +  - compatible
> +  - reg
> +  - dma-ranges
> +  - "#interconnect-cells"
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    dram-controller@0 {

Either dma-controller or memory-controller, decide what is this.

> +        compatible = "spacemit,k1-mbus";
> +        reg = <0x00000000 0x80000000>;
> +        dma-ranges = <0x00000000 0x00000000 0x80000000>;
> +        #address-cells = <1>;
> +        #size-cells = <1>;

Nothing improved.

> +        #interconnect-cells = <0>;
> +    };
> 
> -- 
> 2.49.0
>