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SubjectRe: [PATCH] dt-bindings: i2c: add bindings for nxp,pca9541
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On 06/27/2016 03:11 AM, Peter Rosin wrote:
> Fill the gap for this pre-existing driver.
>
> Signed-off-by: Peter Rosin <peda@axentia.se>
> ---
> .../devicetree/bindings/i2c/i2c-arb-pca9541.txt | 33 ++++++++++++++++++++++
> MAINTAINERS | 1 +
> 2 files changed, 34 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/i2c/i2c-arb-pca9541.txt
>
> Hi!
>
> I'm wondering about this driver. It is not a trivial device, and yet it
> has historically relied on the i2c core matching the chip w/o vendor
> prefix. This is not ideal. But what to do about the driver implementing
> this in terms of an i2c-mux, somthing which the chip is not; It is an
> i2c arbitrator. It just happens to rely on the i2c mux core also handling
> i2c gates and i2c arbitrators. But that seems like a Linux detail. So I
> don't know what to do here?
>

The concept of arbitrators didn't exist when I wrote the driver. I would not
have a problem with renaming the file if that is what you are asking for.

> That is, the patch - as is - describes something that would be trivial to
> support today, but at the same time it seems to be too tied to Linux.
>
> The problem is that the i2c@0 intermediate node is not really needed, but
> at the same time removing it would cause a disruption for the driver since
> it can't really use the i2c mux core if that node isn't there. I don't
> see a simple way to fix that in the i2c mux core either (but admittedly
> haven't given it too much thought).
>

The gpio arbitrator uses the same principle as well. Why not just leave it
alone ? Besides, I think it is a good idea to have it, since it groups
the i2c devices behind the chip together. I would not consider that to be
a Linuxism, but a design choice.

Guenter

> Any suggestions?
>
> Cheers,
> Peter
>
> PS. The driver source is in drivers/i2c/muxes/i2c-mux-pca9541.c
>
> diff --git a/Documentation/devicetree/bindings/i2c/i2c-arb-pca9541.txt b/Documentation/devicetree/bindings/i2c/i2c-arb-pca9541.txt
> new file mode 100644
> index 000000000000..edbe84935906
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/i2c/i2c-arb-pca9541.txt
> @@ -0,0 +1,33 @@
> +* NXP PCA9541 I2C bus master selector
> +
> +Required Properties:
> +
> + - compatible: Must be "nxp,pca9541"
> +
> + - reg: The I2C address of the device.
> +
> + The following required properties are defined externally:
> +
> + - Standard I2C mux properties. See i2c-mux.txt in this directory.
> + - I2C child bus nodes. See i2c-mux.txt in this directory.
> +
> +
> +Example:
> +
> + i2c-arbitrator@74 {
> + compatible = "nxp,pca9541";
> + #address-cells = <1>;
> + #size-cells = <0>;
> + reg = <0x74>;
> +
> + i2c@0 {
> + #address-cells = <1>;
> + #size-cells = <0>;
> + reg = <0>;
> +
> + eeprom@54 {
> + compatible = "at,24c08";
> + reg = <0x54>;
> + };
> + };
> + };
> diff --git a/MAINTAINERS b/MAINTAINERS
> index e1b090f86e0d..3dd44d0d166c 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -5521,6 +5521,7 @@ S: Maintained
> F: Documentation/i2c/i2c-topology
> F: Documentation/i2c/muxes/
> F: Documentation/devicetree/bindings/i2c/i2c-mux*
> +F: Documentation/devicetree/bindings/i2c/i2c-arb*
> F: drivers/i2c/i2c-mux.c
> F: drivers/i2c/muxes/
> F: include/linux/i2c-mux.h
>

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