linux-kernel - Re: [PATCH v2] dt-bindings: spi: convert Freescale DSPI to dt-schema

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Message-ID: <c9b82051-a9f5-883f-5455-1cb06aa6521b@linaro.org>
Date:   Tue, 15 Nov 2022 15:08:37 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Vladimir Oltean <olteanv@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Kuldeep Singh <singh.kuldeep87k@...il.com>,
        Michael Walle <michael@...le.cc>,
        Kuldeep Singh <kuldeep.singh@....com>
Subject: Re: [PATCH v2] dt-bindings: spi: convert Freescale DSPI to dt-schema

On 15/11/2022 14:59, Vladimir Oltean wrote:
> On Tue, Nov 15, 2022 at 02:46:21PM +0100, Krzysztof Kozlowski wrote:
>>> +$id: http://devicetree.org/schemas/spi/fsl,spi-fsl-dspi.yaml
>>
>> Why second "fsl" in file name? It does not patch compatibles and
>> duplicates the vendor. We do not have compatibles "nxp,imx6-nxp".
> 
> Ok, which file name would be good then? There are 9 different (all SoC
> specific) compatible strings, surely the convention of naming the file
> after a compatible string has some limitations...

If all DSPI blocks fit here, then maybe: fsl,dspi.yaml

fsl,spi-dspi.yaml is also a bit redundant.

> 
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml
>>> +
>>> +title: Freescale DSPI Controller
>>> +
>>> +maintainers:
>>> +  - Vladimir Oltean <olteanv@...il.com>
>>> +
>>> +allOf:
>>> +  - $ref: "spi-controller.yaml#"
>>
>> Drop quotes.
>>
>>> +
>>> +properties:
>>> +  compatible:
>>> +    description:
>>> +      Some integrations can have a single compatible string containing their
>>> +      SoC name (LS1012A, LS1021A, ...). Others require their SoC compatible
>>> +      string, plus a fallback compatible string (either on LS1021A or on
>>> +      LS2085A).
>>
>> Why? The fsl,ls1012a-dspi device is either compatible with
>> fsl,ls1021a-v1.0-dspi or not. It cannot be both - compatible and not
>> compatible.
> 
> LS1012A is compatible with LS1021A to the extent that it works when
> treated like a LS1021A. LS1012A has a FIFO size of 8 SPI words, LS1021A
> of just 4. Treating it like LS1021A means roughly half the performance,
> but it still works.
> 
> I didn't invent any of this. When I took over the driver, there were
> device trees like this all over the place:
> 
> 		dspi: spi@...0000 {
> 			compatible = "fsl,ls1012a-dspi", "fsl,ls1021a-v1.0-dspi";

Which looks ok...

> 			#address-cells = <1>;
> 			#size-cells = <0>;
> 			reg = <0x0 0x2100000 0x0 0x10000>;
> 			interrupts = <0 64 IRQ_TYPE_LEVEL_HIGH>;
> 			clock-names = "dspi";
> 			clocks = <&clockgen QORIQ_CLK_PLATFORM_PLL
> 					    QORIQ_CLK_PLL_DIV(1)>;
> 			spi-num-chipselects = <5>;
> 			big-endian;
> 			status = "disabled";
> 		};
> 
> but the Linux driver pre-~5.7 always relied on the fallback compatible
> string (LS1021A in this case). I'm working with what's out in the field,
> haven't changed a thing there.

The driver matters less (except ABI), but anyway it confirms the case -
fallback is expected always.  Why the fallback should be removed if the
devices are compatible (including halved performance)?

> 
>>> +    oneOf:
>>> +      - enum:
>>> +          - fsl,ls1012a-dspi
>>> +          - fsl,ls1021a-v1.0-dspi
>>> +          - fsl,ls1028a-dspi
>>> +          - fsl,ls2085a-dspi
>>> +          - fsl,lx2160a-dspi
>>> +          - fsl,vf610-dspi
>>> +      - items:
>>> +          - enum:
>>> +              - fsl,ls1012a-dspi
>>> +              - fsl,ls1028a-dspi
>>> +              - fsl,ls1043a-dspi
>>> +              - fsl,ls1046a-dspi
>>> +              - fsl,ls1088a-dspi
>>> +          - const: fsl,ls1021a-v1.0-dspi
>>> +      - items:
>>> +          - enum:
>>> +              - fsl,ls2080a-dspi
>>> +              - fsl,lx2160a-dspi
>>> +          - const: fsl,ls2085a-dspi
>>> +
>>> +  reg:
>>> +    maxItems: 1
>>> +
>>> +  interrupts:
>>> +    maxItems: 1
>>> +
>>> +  clocks:
>>> +    maxItems: 1
>>> +
>>> +  clock-names:
>>> +    items:
>>> +      - const: dspi
>>> +
>>> +  dmas:
>>> +    maxItems: 2
>>> +
>>> +  dma-names:
>>> +    items:
>>> +      - const: tx
>>> +      - const: rx
>>> +
>>> +  spi-num-chipselects:
>>
>> Would be nice to deprecated it in separate patches. There is num-cs
>> property.
> 
> Will add this on my TODO list. Right now I'm just converting what exists.

Sure.

Best regards,
Krzysztof