Re: [PATCH v11 1/7] i2c: add I2C Address Translator (ATR) support

Rob Herring
2023-04-25T17:13:57Z

On Fri, Apr 21, 2023 at 01:18:27PM +0300, Tomi Valkeinen wrote:
> From: Luca Ceresoli <luca@lucaceresoli.net>
>
> An ATR is a device that looks similar to an i2c-mux: it has an I2C
> slave "upstream" port and N master "downstream" ports, and forwards
> transactions from upstream to the appropriate downstream port. But it
> is different in that the forwarded transaction has a different slave
> address. The address used on the upstream bus is called the "alias"
> and is (potentially) different from the physical slave address of the
> downstream chip.
>
> Add a helper file (just like i2c-mux.c for a mux or switch) to allow
> implementing ATR features in a device driver. The helper takes care or
> adapter creation/destruction and translates addresses at each transaction.
>
> Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
> .../devicetree/bindings/i2c/i2c-atr.yaml | 34 +
> Documentation/i2c/i2c-address-translators.rst | 96 +++
> Documentation/i2c/index.rst | 1 +
> MAINTAINERS | 8 +
> drivers/i2c/Kconfig | 9 +
> drivers/i2c/Makefile | 1 +
> drivers/i2c/i2c-atr.c | 684 ++++++++++++++++++
> include/linux/i2c-atr.h | 116 +++
> 8 files changed, 949 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/i2c/i2c-atr.yaml
> create mode 100644 Documentation/i2c/i2c-address-translators.rst
> create mode 100644 drivers/i2c/i2c-atr.c
> create mode 100644 include/linux/i2c-atr.h
>
> diff --git a/Documentation/devicetree/bindings/i2c/i2c-atr.yaml b/Documentation/devicetree/bindings/i2c/i2c-atr.yaml
> new file mode 100644
> index 000000000000..d7f73d98110d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/i2c/i2c-atr.yaml
> @@ -0,0 +1,34 @@
> +# SPDX-License-Identifier: GPL-2.0

Dual license.

> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/i2c/i2c-atr.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Common i2c address translator properties.

Drop hard stop.

> +
> +maintainers:
> + - Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
> +
> +description:
> + An I2C Address Translator (ATR) is a device with an I2C slave parent
> + ("upstream") port and N I2C master child ("downstream") ports, and
> + forwards transactions from upstream to the appropriate downstream port
> + with a modified slave address. The address used on the parent bus is
> + called the "alias" and is (potentially) different from the physical
> + slave address of the child bus. Address translation is done by the
> + hardware.
> +
> +properties:
> + i2c-alias-pool:
> + $ref: /schemas/types.yaml#/definitions/uint16-array

We do support some flags in the upper 16-bits of I2C addresses. Any of
those possibly needed here?

> + description:
> + I2C alias pool is a pool of I2C addresses on the main I2C bus that can be
> + used to access the remote peripherals on the serializer's I2C bus. The
> + addresses must be available, not used by any other peripheral. Each
> + remote peripheral is assigned an alias from the pool, and transactions to
> + that address will be forwarded to the remote peripheral, with the address
> + translated to the remote peripheral's real address. This property is not
> + needed if there are no I2C addressable remote peripherals.
> +
> +additionalProperties: true
> +...