Re: [PATCH] dt-bindings: misc: add schema for xlnx,axi-fifo-mm-s

[Conor Dooley]

On Fri, Feb 27, 2026 at 02:30:44PM -0300, Lucas Faria Mendes wrote:
> Add a proper YAML devicetree binding schema for the Xilinx AXI-Stream
> FIFO IP core, documenting the three supported compatible strings:
> xlnx,axi-fifo-mm-s-4.1, xlnx,axi-fifo-mm-s-4.2, and
> xlnx,axi-fifo-mm-s-4.3.
> 
> This resolves the checkpatch warnings about undocumented DT compatible
> strings.
> 
> Signed-off-by: Lucas Faria Mendes <lucas.fariamo08@xxxxxxxxx>
> ---
>  .../bindings/misc/xlnx,axi-fifo-mm-s.yaml     | 102 ++++++++++++++++++
>  1 file changed, 102 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/misc/xlnx,axi-fifo-mm-s.yaml
> 
> diff --git a/Documentation/devicetree/bindings/misc/xlnx,axi-fifo-mm-s.yaml b/Documentation/devicetree/bindings/misc/xlnx,axi-fifo-mm-s.yaml
> new file mode 100644
> index 000000000000..dbb5425e39d6
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/misc/xlnx,axi-fifo-mm-s.yaml
> @@ -0,0 +1,102 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/misc/xlnx,axi-fifo-mm-s.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Xilinx AXI-Stream FIFO IP core
> +
> +maintainers:
> +  - Jacob Feder <jacobsfeder@xxxxxxxxx>
> +
> +description: |
> +  The Xilinx AXI-Stream FIFO IP core has read and write AXI-Stream FIFOs,
> +  the contents of which can be accessed from the AXI4 memory-mapped interface.
> +  This is useful for transferring data from a processor into the FPGA fabric.

Isn't this basically a dma controller?

> +  The driver creates a character device that can be read/written to with
> +  standard open/read/write/close.

This has nothing to do with the binding. I went looking for the driver
and realised it is in staging, and there's a text binding in staging
which this patch should be deleting!
Are you trying to get this out of staging? I don't know how much value
there is in trying to convert the binding if the driver isn't going to
be moved out.

> +
> +  See Xilinx PG080 document for IP details.
> +
> +  Currently supports only store-forward mode with a 32-bit AXI4-Lite
> +  interface.
> +
> +properties:
> +  compatible:
> +    enum:
> +      - xlnx,axi-fifo-mm-s-4.1
> +      - xlnx,axi-fifo-mm-s-4.2
> +      - xlnx,axi-fifo-mm-s-4.3

I find it kinda suspect that minor version changes cause incompatible
changes in the programming model.

> +
> +  reg:
> +    maxItems: 1
> +
> +  interrupts:
> +    maxItems: 1
> +
> +  interrupt-names:
> +    items:
> +      - const: interrupt
> +
> +  xlnx,axi-str-rxd-tdata-width:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    const: 32
> +    description:
> +      AXI-Stream RX data width in bits. Only 32-bit is supported.
> +
> +  xlnx,axi-str-txd-tdata-width:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    const: 32
> +    description:
> +      AXI-Stream TX data width in bits. Only 32-bit is supported.

Why do these need properties if they are only 32-bit always? Is that
limitation on the driver? If so, the binding should permit what the
hardware can do.

> +
> +  xlnx,rx-fifo-depth:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description:
> +      Depth of RX FIFO in words.
> +
> +  xlnx,tx-fifo-depth:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description:
> +      Depth of TX FIFO in words.
> +
> +  xlnx,use-rx-data:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    enum: [0, 1]
> +    description:
> +      1 if RX FIFO is enabled, 0 otherwise.

These two should be booleans.

> +
> +  xlnx,use-tx-data:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    enum: [0, 1]
> +    description:
> +      1 if TX FIFO is enabled, 0 otherwise.
> +
> +required:
> +  - compatible
> +  - reg
> +  - interrupts
> +  - xlnx,axi-str-rxd-tdata-width
> +  - xlnx,axi-str-txd-tdata-width
> +  - xlnx,rx-fifo-depth
> +  - xlnx,tx-fifo-depth
> +  - xlnx,use-rx-data
> +  - xlnx,use-tx-data

And if the properties become boolean, they aren't required any more.

> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    axi_fifo_mm_s@43c00000 {

I think this should be "dma-controller".

> +        compatible = "xlnx,axi-fifo-mm-s-4.1";
> +        interrupt-names = "interrupt";
> +        interrupt-parent = <&intc>;
> +        interrupts = <0 29 4>;
> +        reg = <0x43c00000 0x10000>;

reg should be after properties.

pw-bot: changes-requested

Thanks,
Conor.

> +        xlnx,axi-str-rxd-tdata-width = <0x20>;
> +        xlnx,axi-str-txd-tdata-width = <0x20>;
> +        xlnx,rx-fifo-depth = <0x200>;
> +        xlnx,tx-fifo-depth = <0x8000>;
> +        xlnx,use-rx-data = <0x0>;
> +        xlnx,use-tx-data = <0x1>;
> +    };
> -- 
> 2.53.0
>

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