linux-kernel - Re: [PATCH 2/2] dt-bindings: fpga: add binding doc for ecp5-spi fpga mgr

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Date:   Fri, 15 Jul 2022 13:03:56 +0300
From:   Ivan Bornyakov <i.bornyakov@...rotek.ru>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     mdf@...nel.org, hao.wu@...el.com, yilun.xu@...el.com,
        trix@...hat.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, linux-fpga@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        system@...rotek.ru
Subject: Re: [PATCH 2/2] dt-bindings: fpga: add binding doc for ecp5-spi fpga
 mgr

On Fri, Jul 15, 2022 at 11:33:54AM +0200, Krzysztof Kozlowski wrote:
> On 14/07/2022 14:26, Ivan Bornyakov wrote:
> > Add Device Tree Binding doc for Lattice ECP5 FPGA manager using slave
> > SPI to load .bit formatted uncompressed bitstream image.
> > 
> > Signed-off-by: Ivan Bornyakov <i.bornyakov@...rotek.ru>
> > ---
> >  .../fpga/lattice,ecp5-spi-fpga-mgr.yaml       | 71 +++++++++++++++++++
> >  1 file changed, 71 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/fpga/lattice,ecp5-spi-fpga-mgr.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/fpga/lattice,ecp5-spi-fpga-mgr.yaml b/Documentation/devicetree/bindings/fpga/lattice,ecp5-spi-fpga-mgr.yaml
> > new file mode 100644
> > index 000000000000..79868f9c84e2
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/fpga/lattice,ecp5-spi-fpga-mgr.yaml
> > @@ -0,0 +1,71 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/fpga/lattice,ecp5-spi-fpga-mgr.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Lattice ECP5 FPGA manager.
> > +
> > +maintainers:
> > +  - Ivan Bornyakov <i.bornyakov@...rotek.ru>
> > +
> > +description:
> > +  Device Tree Bindings for Lattice ECP5 FPGA Manager using slave SPI to
> > +  load the uncompressed bitstream in .bit format.
> 
> s/Device Tree Bindings for//
> 
> Instead describe the hardware you are adding bindings for. What is a
> "Manager"? It is so broad and unspecific... It is some dedicated
> hardware to communicate with FPGA or you just called this regular FPGA
> interface exposed to the CPU/SoC?
> 

"FPGA Manager" is a kernel subsystem that exports a set of functions for
programming an FPGA with a bitstream image.
See Documentation/driver-api/fpga/fpga-mgr.rst

> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - lattice,ecp5-spi-fpga-mgr
> 
> Do not encode interface name in compatible so no "spi".
> 

Recently when I submitted FPGA manager for Microchip PolarFire, I was
asked the opposite, to add "spi" in compatible. The reason was that FPGA
can be programmed through other interfaces as well.

> > +
> > +  reg:
> > +    description: SPI chip select
> > +    maxItems: 1
> > +
> > +  spi-max-frequency:
> > +    maximum: 60000000
> 
> Reference spi/spi-peripheral-props.yaml in allOf
> 
> > +
> > +  program-gpios:
> > +    description:
> > +      A GPIO line connected to PROGRAMN (active low) pin of the device.
> > +      Initiates configuration sequence.
> > +    maxItems: 1
> > +
> > +  init-gpios:
> > +    description:
> > +      A GPIO line connected to INITN (active low) pin of the device.
> > +      Indicates the FPGA is ready to be configured.
> > +    maxItems: 1
> > +
> > +  done-gpios:
> > +    description:
> > +      A GPIO line connected to DONE (active high) pin of the device.
> > +      Indicates that the configuration sequence is complete.
> > +    maxItems: 1
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - program-gpios
> > +  - init-gpios
> > +  - done-gpios
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    #include <dt-bindings/gpio/gpio.h>
> > +
> > +    spi {
> > +            #address-cells = <1>;
> 
> Wrong indentation. 4-spaces for DTS example.
> 
> > +            #size-cells = <0>;
> > +
> > +            fpga_mgr@0 {
> 
> No underscores in node names.
> 
> > +                    compatible = "lattice,ecp5-spi-fpga-mgr";
> > +                    spi-max-frequency = <20000000>;
> > +                    reg = <0>;
> > +                    program-gpios = <&gpio3 4 GPIO_ACTIVE_LOW>;
> > +                    init-gpios = <&gpio3 3 GPIO_ACTIVE_LOW>;
> > +                    done-gpios = <&gpio3 2 GPIO_ACTIVE_HIGH>;
> > +            };
> > +    };
> 
> 
> Best regards,
> Krzysztof