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

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Date:   Tue, 15 Nov 2022 14:19:04 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
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 Tue, Nov 15, 2022 at 03:08:37PM +0100, Krzysztof Kozlowski wrote:
> 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.

Ok, fsl,dspi.yaml and fsl,dspi-peripheral-props.yaml, and MAINTAINERS
entry for fsl,dspi*.yaml?

> >>> +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)?

I don't think I said the fallback should be removed? I think you're
talking about a typo/braino I made, which puts the LS1012A both in the
bucket of SoCs with a single compatible strings required, as well as in
that with fallback required. Obviously both can't be true... I didn't
mean LS1012A but VF610.