linux-kernel - Re: [PATCH 1/3] dt-bindings: spi: add SpacemiT K1 SPI support

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Message-ID: <20250918195716.GA2521514-robh@kernel.org>
Date: Thu, 18 Sep 2025 14:57:16 -0500
From: Rob Herring <robh@...nel.org>
To: Alex Elder <elder@...cstar.com>
Cc: Yixun Lan <dlan@...too.org>, broonie@...nel.org, krzk+dt@...nel.org,
	conor+dt@...nel.org, linux-spi@...r.kernel.org,
	devicetree@...r.kernel.org, paul.walmsley@...ive.com,
	palmer@...belt.com, aou@...s.berkeley.edu, alex@...ti.fr,
	p.zabel@...gutronix.de, spacemit@...ts.linux.dev,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] dt-bindings: spi: add SpacemiT K1 SPI support

On Wed, Sep 17, 2025 at 06:40:31PM -0500, Alex Elder wrote:
> On 9/17/25 6:15 PM, Yixun Lan wrote:
> > Hi Alex,
> > 
> > On 17:07 Wed 17 Sep     , Alex Elder wrote:
> > > Add support for the SPI controller implemented by the SpacemiT K1 SoC.
> > > 
> > > Signed-off-by: Alex Elder <elder@...cstar.com>
> > > ---
> > >   .../bindings/spi/spacemit,k1-spi.yaml         | 94 +++++++++++++++++++
> > >   1 file changed, 94 insertions(+)
> > >   create mode 100644 Documentation/devicetree/bindings/spi/spacemit,k1-spi.yaml
> > > 
> > > diff --git a/Documentation/devicetree/bindings/spi/spacemit,k1-spi.yaml b/Documentation/devicetree/bindings/spi/spacemit,k1-spi.yaml
> > > new file mode 100644
> > > index 0000000000000..5abd4fe268da9
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/spi/spacemit,k1-spi.yaml
> > > @@ -0,0 +1,94 @@
> > > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > > +%YAML 1.2
> > > +---
> > > +$id: http://devicetree.org/schemas/spi/spacemit,k1-spi.yaml#
> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > +
> > > +title: SpacemiT K1 SoC Serial Peripheral Interface (SPI)
> > > +
> > > +maintainers:
> > > +  - Alex Elder <elder@...nel.org>
> > > +
> > > +description:
> > > +  The SpacemiT K1 SoC implements a SPI controller that has two 32-entry
> > > +  FIFOs, for transmit and receive.  Details are currently available in
> > > +  section 18.2.1 of the K1 User Manual, found in the SpacemiT Keystone
> > > +  K1 Documentation[1].  The controller transfers words using PIO.  DMA
> > > +  transfers are supported as well, if both TX and RX DMA channels are
> > > +  specified,
> > > +
> > > +  [1] https://developer.spacemit.com/documentation
> > > +
> > > +allOf:
> > > +  - $ref: /schemas/spi/spi-controller.yaml#
> > > +
> > > +properties:
> > > +  compatible:
> > > +    enum:
> > > +      - spacemit,k1-spi
> > one enum is effectively equal to const..
> 
> OK.  That's an easy fix.
> 
> > > +
> > > +  reg:
> > > +    maxItems: 1
> > > +
> > > +  clocks:
> > > +    items:
> > > +      - description: Core clock
> > > +      - description: Bus clock
> > > +
> > > +  clock-names:
> > > +    items:
> > > +      - const: core
> > > +      - const: bus
> > > +
> > > +  resets:
> > > +    maxItems: 1
> > > +
> > > +  interrupts:
> > > +    maxItems: 1
> > > +
> > > +  dmas:
> > > +    items:
> > > +      - description: RX DMA channel
> > > +      - description: TX DMA channel
> > > +
> > > +  dma-names:
> > > +    items:
> > > +      - const: rx
> > > +      - const: tx
> > > +
> > > +  spacemit,k1-ssp-id:
> > > +    description: SPI controller number
> > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > could you explain a little bit why this vendor specific property should
> > be introduced? I took a look at the code, and didn't get the reason
> > behind.. or what's the problem of simply using "pdev->id"?
> 
> This property was carried over from the vendor code.  It is
> optional, and if it isn't specified, the platform device ID (-1)
> will be used.  It's just intended to provide a well-defined ID
> for a particular SPI controller.
> 
> > we should really be careful to introduce vendor specific property..
> 
> If there were a standard way of doing this I'd love to use it.

The standard way is we don't define made up device indices in DT. Well, 
except /aliases allows you to do that.

Rob