Re: [PATCH 1/2] dt-bindings: spi: Add Baikal-T1 System Boot SPI Controller binding

[Rob Herring <robh@kernel.org>]

On Fri, May 08, 2020 at 12:36:20PM +0300, Serge Semin wrote:
> Baikal-T1 Boot SPI is a part of the SoC System Controller and is
> responsible for the system bootup from an external SPI flash. It's a DW
> APB SSI-based SPI-controller with no interrupts, no DMA, with just one
> native chip-select available and a single reference clock. Since Baikal-T1
> SoC is normally booted up from an external SPI flash this SPI controller
> in most of the cases is supposed to be connected to a single SPI-nor
> flash. Additionally in order to provide a transparent from CPU point of
> view initial code execution procedure the system designers created an IP
> block which physically maps the SPI flash found at CS0 to a memory region.
> 
> Co-developed-by: Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru>
> Signed-off-by: Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru>
> Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> Cc: Paul Burton <paulburton@kernel.org>
> Cc: Ralf Baechle <ralf@linux-mips.org>
> Cc: John Garry <john.garry@huawei.com>
> Cc: Chuanhong Guo <gch981213@gmail.com>
> Cc: Tomer Maimon <tmaimon77@gmail.com>
> Cc: Lee Jones <lee.jones@linaro.org>
> Cc: Miquel Raynal <miquel.raynal@bootlin.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: linux-mips@vger.kernel.org
> Cc: linux-spi@vger.kernel.org
> ---
>  .../bindings/spi/baikal,bt1-sys-ssi.yaml      | 100 ++++++++++++++++++
>  1 file changed, 100 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/spi/baikal,bt1-sys-ssi.yaml
> 
> diff --git a/Documentation/devicetree/bindings/spi/baikal,bt1-sys-ssi.yaml b/Documentation/devicetree/bindings/spi/baikal,bt1-sys-ssi.yaml
> new file mode 100644
> index 000000000000..d9d3257d78f4
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/spi/baikal,bt1-sys-ssi.yaml
> @@ -0,0 +1,100 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +# Copyright (C) 2020 BAIKAL ELECTRONICS, JSC
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/spi/baikal,bt1-sys-ssi.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Baikal-T1 System Boot SSI Controller
> +
> +description: |
> +  Baikal-T1 System Controller includes a Boot SPI Controller, which is
> +  responsible for loading chip bootup code from an external SPI flash. In order
> +  to do this transparently from CPU point of view there is a dedicated IP block
> +  mapping the 16MB flash to a dedicated MMIO range. The controller is based on
> +  the DW APB SSI IP-core but equipped with very limited resources: no IRQ,
> +  no DMA, a single native CS being necessarily connected to a 16MB SPI flash
> +  (otherwise the system won't bootup from the flash), internal Tx/Rx FIFO of
> +  just 8 bytes depth. Access to DW APB SSI controller registers is mutually
> +  exclusive from normal MMIO interface and from physically mapped SPI Flash
> +  memory. So either one or another way of using the controller functionality
> +  can be enabled at a time.
> +
> +maintainers:
> +  - Serge Semin <fancer.lancer@gmail.com>
> +
> +allOf:
> +  - $ref: spi-controller.yaml#
> +
> +properties:
> +  compatible:
> +    const: baikal,bt1-sys-ssi
> +
> +  reg:
> +    items:
> +      - description: Baikal-T1 Boot Controller configuration registers
> +      - description: Physically mapped SPI flash ROM found at CS0
> +
> +  reg-names:
> +    items:
> +      - const: config
> +      - const: map
> +
> +  clocks:
> +    description: SPI Controller reference clock source

Can drop this. 

> +    maxItems: 1
> +
> +  clock-names:
> +    items:
> +      - const: ssi_clk
> +
> +  num-cs:
> +    const: 1
> +
> +patternProperties:
> +  "^.*@[0-9a-f]+":
> +    type: object
> +    properties:
> +      reg:
> +        minimum: 0
> +        maximum: 0
> +
> +      spi-rx-bus-width:
> +        const: 1
> +
> +      spi-tx-bus-width:
> +        const: 1

What's the point of these 2 properties if they aren't required?

> +
> +unevaluatedProperties: false
> +
> +required:
> +  - compatible
> +  - reg
> +  - reg-names

> +  - "#address-cells"
> +  - "#size-cells"

These 2 are required by spi-controller.yaml, so you can drop here.

> +  - clocks
> +
> +examples:
> +  - |
> +    spi@1f040000 {
> +      compatible = "baikal,bt1-sys-ssi";
> +      reg = <0x1f040000 0x1000>,
> +            <0x1c000000 0x1000000>;
> +      reg-names = "config", "map";
> +      #address-cells = <1>;
> +      #size-cells = <0>;
> +
> +      clocks = <&ccu_sys>;
> +      clock-names = "ssi_clk";
> +
> +      boot_flash: flash@0 {
> +        compatible = "jedec,spi-nor";
> +        #address-cells = <1>;
> +        #size-cells = <1>;
> +        reg = <0>;
> +
> +        spi-max-frequency = <25000000>;
> +      };
> +    };
> +...
> -- 
> 2.25.1
>