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 <ryan_chen@aspeedtech.com>
---
 .../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.
+        - "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
+
+  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

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 <ryan_chen@aspeedtech.com>
> ---
>  .../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.

> +        - "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.

> +
> +  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
>