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From:   Vladimir Oltean <vladimir.oltean@nxp.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
CC:     "linux-spi@vger.kernel.org" <linux-spi@vger.kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Vladimir Oltean <olteanv@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        Kuldeep Singh <singh.kuldeep87k@gmail.com>,
        Michael Walle <michael@walle.cc>,
        Kuldeep Singh <kuldeep.singh@nxp.com>
Subject: Re: [PATCH v2] dt-bindings: spi: convert Freescale DSPI to dt-schema
Thread-Topic: [PATCH v2] dt-bindings: spi: convert Freescale DSPI to dt-schema
Thread-Index: AQHY9h+FTOIdILG+UESwpW9mF9x8Sq5ABQqAgAADlwCAAAKigIAAAusA
Date:   Tue, 15 Nov 2022 14:19:04 +0000
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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".
> >=20
> > 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...
>=20
> If all DSPI blocks fit here, then maybe: fsl,dspi.yaml
>=20
> 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 containi=
ng their
> >>> +      SoC name (LS1012A, LS1021A, ...). Others require their SoC com=
patible
> >>> +      string, plus a fallback compatible string (either on LS1021A o=
r 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.
> >=20
> > 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.
> >=20
> > I didn't invent any of this. When I took over the driver, there were
> > device trees like this all over the place:
> >=20
> > 		dspi: spi@2100000 {
> > 			compatible =3D "fsl,ls1012a-dspi", "fsl,ls1021a-v1.0-dspi";
>=20
> Which looks ok...
>=20
> > 			#address-cells =3D <1>;
> > 			#size-cells =3D <0>;
> > 			reg =3D <0x0 0x2100000 0x0 0x10000>;
> > 			interrupts =3D <0 64 IRQ_TYPE_LEVEL_HIGH>;
> > 			clock-names =3D "dspi";
> > 			clocks =3D <&clockgen QORIQ_CLK_PLATFORM_PLL
> > 					    QORIQ_CLK_PLL_DIV(1)>;
> > 			spi-num-chipselects =3D <5>;
> > 			big-endian;
> > 			status =3D "disabled";
> > 		};
> >=20
> > 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.
>=20
> 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.=