RE: [PATCH v26 2/4] dt-bindings: i2c: ast2600-i2c.yaml: Add global-regs and transfer-mode properties

> Subject: Re: [PATCH v26 2/4] dt-bindings: i2c: ast2600-i2c.yaml: Add global-regs
> and transfer-mode properties
> 
> On Mon, Mar 09, 2026 at 02:53:53PM +0800, Ryan Chen wrote:
> > The AST2600 I2C controller supports three transfer modes (byte,
> > buffer, DMA). Add "aspeed,transfer-mode" so DT can select the
> > preferred transfer method per controller instance. Also add the
> "aspeed,global-regs"
> > phandle to reference the AST2600 global registers syscon/regmap used
> > by the controller.
> >
> > These properties apply only to the AST2600 binding and are not part of
> > the legacy binding, which uses a mixed controller/target register
> > layout and does not have the split register blocks or these new
> > configuration registers. Legacy DTs remain unchanged.
> >
> > Signed-off-by: Ryan Chen <[email protected]>
> > ---
> >  .../bindings/i2c/aspeed,ast2600-i2c.yaml           | 29
> ++++++++++++++++++++++
> >  1 file changed, 29 insertions(+)
> >
> > diff --git
> > a/Documentation/devicetree/bindings/i2c/aspeed,ast2600-i2c.yaml
> > b/Documentation/devicetree/bindings/i2c/aspeed,ast2600-i2c.yaml
> > index de2c359037da..323e4f9b290a 100644
> > --- a/Documentation/devicetree/bindings/i2c/aspeed,ast2600-i2c.yaml
> > +++ b/Documentation/devicetree/bindings/i2c/aspeed,ast2600-i2c.yaml
> > @@ -37,6 +37,33 @@ properties:
> >    resets:
> >      maxItems: 1
> >
> > +  aspeed,transfer-mode:
> > +    description: |
> > +      ASPEED ast2600 platform equipped with 16 I2C controllers each i2c
> controller
> > +      have 1 byte transfer buffer(byte mode), 32 bytes buffer(buffer mode),
> and
> > +      share a DMA engine.
> > +      Select I2C transfer mode for this controller. Supported values are:
> > +        - "byte": Use 1 byte for i2c transmit (1-byte buffer).
> > +        - "buffer": Use buffer (32-byte buffer) for i2c transmit. (default)
> > +                    Better performance then byte mode.
> 
> Good, I like worse performance so I can use byte mode.
Thanks your review.
Will remove performance statement.
> 
> > +        - "dma": Each controller DMA mode is shared DMA engine. The
> AST2600 SoC
> > +                 provides a single DMA engine shared for 16 I2C
> controllers,
> > +                 so only a limited number of controllers can use DMA
> simultaneously.
> > +                 Therefore, the DTS must explicitly assign which
> controllers are
> > +                 configured to use DMA.
> > +      On AST2600, each controller supports all three modes.
> > +      If not specified, buffer mode is used by default.
> > +    enum:
> > +      - byte
> > +      - buffer
> > +      - dma
> 
> This is not required, so what is the default mode? If there's a default, you don't
> need the default value in the first place as the default is the property omitted.

Thanks, Will update with following.

aspeed,transfer-mode:
  description:
    Selects the AST2600 I2C transfer mode:
      - byte: 1-byte transfer buffer
      - buffer: 32-byte transfer buffer
      - dma: DMA-based transfers
  enum:
    - byte
    - buffer
    - dma
> 
> > +
> > +  aspeed,global-regs:
> > +    $ref: /schemas/types.yaml#/definitions/phandle
> > +    description:
> > +      Phandle reference to the i2c global syscon node, containing the
> > +      SoC-common i2c register set.
> > +
> >  required:
> >    - reg
> >    - compatible
> > @@ -59,4 +86,6 @@ examples:
> >          resets = <&syscon ASPEED_RESET_I2C>;
> >          clock-frequency = <100000>;
> >          interrupts = <GIC_SPI 110 IRQ_TYPE_LEVEL_HIGH>;
> > +        aspeed,global-regs = <&i2c_global>;
> > +        aspeed,transfer-mode = "buffer";
> >      };
> >
> > --
> > 2.34.1
> >