RE: [PATCH v3 2/3] dt-bindings: i2c-ast2600: Add bindings for AST2600 i2C driver

[Ryan Chen]

Hello Andrew,

> -----Original Message-----
> From: Andrew Jeffery <andrew@xxxxxxxx>
> Sent: Friday, July 29, 2022 10:29 AM
> To: Ryan Chen <ryan_chen@xxxxxxxxxxxxxx>; Joel Stanley <joel@xxxxxxxxx>;
> Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> linux-aspeed@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> openbmc@xxxxxxxxxxxxxxxx
> Cc: BMC-SW <BMC-SW@xxxxxxxxxxxxxx>
> 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@xxxxxxxxxxxxxx>
> > ---
> >  .../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@xxxxxxxxxxxxxx>
> > +
> > +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 devicetree.
> 
> 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 though).
> 
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/Makefile#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 = "aspeed,ast2600-i2c-global", "syscon";
> > +      reg = <0x0 0x20>;
> > +      resets = <&syscon ASPEED_RESET_I2C>;
> > +    };
> > +
> > +    i2c0: i2c-bus@80 {
> > +      #address-cells = <1>;
> > +      #size-cells = <0>;
> > +      #interrupt-cells = <1>;
> > +      compatible = "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 ?
If yes, I will start for v4.
> Andrew