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From:   Ryan Chen <ryan_chen@aspeedtech.com>
To:     Andrew Jeffery <andrew@aj.id.au>, Joel Stanley <joel@jms.id.au>,
        Philipp Zabel <p.zabel@pengutronix.de>,
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        "openbmc@lists.ozlabs.org" <openbmc@lists.ozlabs.org>
CC:     BMC-SW <BMC-SW@aspeedtech.com>
Subject: RE: [PATCH v3 2/3] dt-bindings: i2c-ast2600: Add bindings for AST2600
 i2C driver
Thread-Topic: [PATCH v3 2/3] dt-bindings: i2c-ast2600: Add bindings for
 AST2600 i2C driver
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Date:   Tue, 2 Aug 2022 09:04:33 +0000
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Hello,

> -----Original Message-----
> From: Andrew Jeffery <andrew@aj.id.au>
> Sent: Friday, July 29, 2022 11:13 AM
> To: Ryan Chen <ryan_chen@aspeedtech.com>; Joel Stanley <joel@jms.id.au>;
> Philipp Zabel <p.zabel@pengutronix.de>; linux-arm-kernel@lists.infradead.=
org;
> linux-aspeed@lists.ozlabs.org; linux-kernel@vger.kernel.org;
> openbmc@lists.ozlabs.org
> Cc: BMC-SW <BMC-SW@aspeedtech.com>
> Subject: Re: [PATCH v3 2/3] dt-bindings: i2c-ast2600: Add bindings for AS=
T2600
> i2C driver
>=20
>=20
>=20
> On Fri, 29 Jul 2022, at 12:33, Ryan Chen wrote:
> > Hello Andrew,
> >
> >> -----Original Message-----
> >> From: Andrew Jeffery <andrew@aj.id.au>
> >> Sent: Friday, July 29, 2022 10:29 AM
> >> To: Ryan Chen <ryan_chen@aspeedtech.com>; Joel Stanley
> >> <joel@jms.id.au>; Philipp Zabel <p.zabel@pengutronix.de>;
> >> linux-arm-kernel@lists.infradead.org;
> >> linux-aspeed@lists.ozlabs.org; linux-kernel@vger.kernel.org;
> >> openbmc@lists.ozlabs.org
> >> Cc: BMC-SW <BMC-SW@aspeedtech.com>
> >> Subject: Re: [PATCH v3 2/3] dt-bindings: i2c-ast2600: Add bindings
> >> for AST2600 i2C driver
> >>
> >> Hi Ryan,
> >>
> >> On Mon, 16 May 2022, at 16:18, ryan_chen wrote:
> >> > AST2600 support new register set for I2C controller, add bindings
> >> > document to support driver of i2c new register mode controller
> >> >
> >> > Signed-off-by: ryan_chen <ryan_chen@aspeedtech.com>
> >> > ---
> >> >  .../bindings/i2c/aspeed,i2c-ast2600.ymal      | 78
> >> +++++++++++++++++++
> >> >  1 file changed, 78 insertions(+)
> >> >  create mode 100644
> >> > Documentation/devicetree/bindings/i2c/aspeed,i2c-ast2600.ymal
> >> >
> >> > diff --git
> >> > a/Documentation/devicetree/bindings/i2c/aspeed,i2c-ast2600.ymal
> >> > b/Documentation/devicetree/bindings/i2c/aspeed,i2c-ast2600.ymal
> >> > new file mode 100644
> >> > index 000000000000..7c75f5bac24f
> >> > --- /dev/null
> >> > +++ b/Documentation/devicetree/bindings/i2c/aspeed,i2c-ast2600.ymal
> >> > @@ -0,0 +1,78 @@
> >> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) %YAML
> >> > +1.2
> >> > +---
> >> > +$id: http://devicetree.org/schemas/i2c/aspeed,i2c-ast2600.yaml#
> >> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> >> > +
> >> > +title: AST2600 I2C Controller on the AST26XX SoCs Device Tree
> >> > +Bindings
> >> > +
> >> > +maintainers:
> >> > +  - Ryan Chen <ryan_chen@aspeedtech.com>
> >> > +
> >> > +allOf:
> >> > +  - $ref: /schemas/i2c/i2c-controller.yaml#
> >> > +
> >> > +properties:
> >> > +  compatible:
> >> > +    enum:
> >> > +      - aspeed,ast2600-i2c
> >>
> >> The original driver uses e.g. aspeed,ast2500-i2c-bus for the
> >> subordinate controllers. While the register layout changes, I'd
> >> prefer we try to use the existing compatibles rather than introducing
> >> a new set and causing some confusion.
> >>
> >> Further, what you're proposing here is effectively being used to
> >> select the driver implementation, which isn't the purpose of the devic=
etree.
> >>
> >> My preference would be to reuse the existing compatibles and instead
> >> select the driver implementation via Kconfig. Or, if we can figure
> >> out some way to do so, support both register interfaces in the one
> >> driver implementation and fall back to the old register interface
> >> where the new one isn't available (I don't think this is feasible thou=
gh).
> >>
> > Yes, that the reason go for another driver ast2600 to implement.
> > Like others SOC driver implement different generation have diff driver
> > in Kconfig and Makefile.
> > Example :
> > https://github.com/torvalds/linux/blob/master/drivers/i2c/busses/Makef
> > ile#L82-L84
> >
> >
> >> > +
> >> > +  reg:
> >> > +    minItems: 1
> >> > +    items:
> >> > +      - description: address offset and range of bus
> >> > +      - description: address offset and range of bus buffer
> >> > +
> >> > +  interrupts:
> >> > +    maxItems: 1
> >> > +
> >> > +  clocks:
> >> > +    maxItems: 1
> >> > +    description:
> >> > +      root clock of bus, should reference the APB
> >> > +      clock in the second cell
> >> > +
> >> > +  resets:
> >> > +    maxItems: 1
> >> > +
> >> > +  bus-frequency:
> >> > +    minimum: 500
> >> > +    maximum: 2000000
> >> > +    default: 100000
> >> > +    description: frequency of the bus clock in Hz defaults to 100
> >> > + kHz
> >> > when not
> >> > +      specified
> >> > +
> >> > +  multi-master:
> >> > +    type: boolean
> >> > +    description:
> >> > +      states that there is another master active on this bus
> >> > +
> >> > +required:
> >> > +  - reg
> >> > +  - compatible
> >> > +  - clocks
> >> > +  - resets
> >> > +
> >> > +unevaluatedProperties: false
> >> > +
> >> > +examples:
> >> > +  - |
> >> > +    #include <dt-bindings/interrupt-controller/arm-gic.h>
> >> > +    #include <dt-bindings/clock/ast2600-clock.h>
> >> > +
> >> > +    i2c_gr: i2c-global-regs@0 {
> >> > +      compatible =3D "aspeed,ast2600-i2c-global", "syscon";
> >> > +      reg =3D <0x0 0x20>;
> >> > +      resets =3D <&syscon ASPEED_RESET_I2C>;
> >> > +    };
> >> > +
> >> > +    i2c0: i2c-bus@80 {
> >> > +      #address-cells =3D <1>;
> >> > +      #size-cells =3D <0>;
> >> > +      #interrupt-cells =3D <1>;
> >> > +      compatible =3D "aspeed,ast2600-i2c-bus";
> >>
> >> This isn't quite right with respect to your binding description above
> >> :)
> > Yes, the compatible need to be " aspeed,ast2600-i2c" is that your point=
 ?
>=20
> Yes, but only if we agree that we should have different compatibles for t=
he
> different drivers. I'm not convinced about that yet.
>=20
> I think it's enough to have different Kconfig symbols, and select the old=
 driver
> in aspeed_g4_defconfig, and the new driver in aspeed_g5_defconfig. Won't
> that gives us the right outcome without requiring a new set of compatible=
s?
>=20
The new driver in aspeed_g5_defconfig. And different compatible string clai=
m will
Load the new or legacy driver, it should ok like the different generation S=
OC. Have=20
different design.
Am I right?

> Andrew