linux-kernel - Re: [PATCH 3/8] dt-bindings: spi: Add Nuvoton WPCM450 Flash Interface Unit (FIU)

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Date:   Mon, 7 Nov 2022 09:09:15 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Jonathan Neuschäfer <j.neuschaefer@....net>
Cc:     linux-spi@...r.kernel.org, openbmc@...ts.ozlabs.org,
        Lee Jones <lee@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-gpio@...r.kernel.org
Subject: Re: [PATCH 3/8] dt-bindings: spi: Add Nuvoton WPCM450 Flash Interface
 Unit (FIU)

On 06/11/2022 15:45, Jonathan Neuschäfer wrote:
> On Sun, Nov 06, 2022 at 10:38:45AM +0100, Krzysztof Kozlowski wrote:
>> On 05/11/2022 19:59, Jonathan Neuschäfer wrote:
>>> The Flash Interface Unit (FIU) is the SPI flash controller in the
>>> Nuvoton WPCM450 BMC SoC. It supports four chip selects, and direct
>>> (memory-mapped) access to 16 MiB per chip. Larger flash chips can be
>>> accessed by software-defined SPI transfers.
>>>
>>> The FIU in newer NPCM7xx SoCs is not compatible with the WPCM450 FIU.
>>>
>>> Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@....net>
>>> ---
> [...]
>>> +allOf:
>>> +  - $ref: "/schemas/spi/spi-controller.yaml#"
>>
>> Drop the quotes.
> 
> Will do.
> 
> 
>>> +
>>> +properties:
>>> +  compatible:
>>> +    const: nuvoton,wpcm450-fiu
>>> +
>>> +  reg:
>>> +    items:
>>> +      - description: FIU registers
>>> +      - description: Memory-mapped flash contents
>>> +
>>> +  reg-names:
>>> +    items:
>>> +      - const: control
>>> +      - const: memory
>>> +    minItems: 1
>>
>> This does not match your 'reg'. Two items are required there.
> 
> My intention was rather to make the second reg item actually optional,
> i.e. add minItems: 1 for reg as well.  (But, further discussion below.)
> 
> 
>>> +    spi@...00000 {
>>> +      compatible = "nuvoton,wpcm450-fiu";
>>> +      #address-cells = <1>;
>>> +      #size-cells = <0>;
>>> +      reg = <0xc8000000 0x1000>, <0xc0000000 0x4000000>;
>>
>> reg is the second property.
> 
> Ok, I'll move it up.
> 
>>
>>> +      reg-names = "control", "memory";
>>> +      clocks = <&clk WPCM450_CLK_FIU>;
>>> +      nuvoton,shm = <&shm>;
>>> +
>>> +      flash@0 {
>>> +        compatible = "jedec,spi-nor";
>>> +      };
>>> +    };
>>> +
>>> +    shm: syscon@...01000 {
>>> +      compatible = "nuvoton,wpcm450-shm", "syscon";
>>> +      reg = <0xc8001000 0x1000>;
>>> +    };
>>> +
>>> +  - |
>>> +    #include <dt-bindings/clock/nuvoton,wpcm450-clk.h>
>>> +    spi@...00000 {
>>> +      compatible = "nuvoton,wpcm450-fiu";
>>> +      // the "memory" resource may be omitted
>>
>> This is rather obvious, so what you should comment is WHY or WHEN second
>> resource can be omitted.
> 
> Ok, I'll add more reasoning, which is basically: The "memory" mapping is
> only an optimization for faster access, knowledge of it is not necessary
> for full operation of the device.
> 
>> Not every instance on the hardware has it?
> 
> AFAIK every instance has it, and there's unlikely to be any variation on
> this fact anymore, because newer Nuvoton SoCs replaced the FIU with a
> redesigned and incompatible version.
> 
> I admit that the value of making the "memory" mapping optional is rather
> theoretical, and I'm open to making this reg item mandatory to simplify
> the binding.

If every instance has it, then regardless whether it is actually used or
not, just require second address?

Best regards,
Krzysztof