[PATCH v3 0/7] Add Mule I2C multiplexer support

[Farouk Bouabid <farouk.bouabid@cherry.de>]

Mule is an mcu that emulates a set of I2C devices which are reachable
through an I2C-mux.

The emulated devices share a single I2C address with the mux itself
where the requested register is what determines which logic is executed
(muxing logic or device logic):

1- The devices on the mux can be selected (muxing functionality) by
writing the appropriate device number to an I2C config register (0xff)
that is not used by any device logic.

2- Any access to a register other than the config register will be
handled by the previously selected device.

      +-------------------------------------------------------+
      |  Mule                                                 |
      |        +---------------+                              |
    ----+-(1)->|Config register|-----+                        |
      | |      +---------------+     |                        |
      | |                            V_                       |
      | |                            |  \          +--------+ |
      | |                            |   \-------->| dev #0 | |
      | |                            |   |         +--------+ |
      | |                            | M |-------->| dev #1 | |
      | +-----------(2)------------->| U |         +--------+ |
      |                              | X |-------->| dev #2 | |
      |                              |   |         +--------+ |
      |                              |   /-------->| dev #3 | |
      |                              |__/          +--------+ |
      +-------------------------------------------------------+

The current I2C-mux implementation does not allow the mux to use the
I2C address of a child device. As a workaround, A new I2C-adapter quirk is
introduced to skip the check for conflict between a child device and the
mux core I2C address when adding the child device.

This patch-series adds support for this multiplexer. Mule is integrated
as part of rk3399-puma, px30-ringneck, rk3588-tiger and rk3588-jaguar
boards.

Signed-off-by: Farouk Bouabid <farouk.bouabid@cherry.de>

Changes in v3:
- Change "i2c" in comments/commit-logs to "I2C"
- Fix long line-length
- Warn when "share_addr_with_children" is set and the Mux is not an I2C device
- Fix/stop propagating "I2C_AQ_SKIP_ADDR_CHECK" flag if "share_addr_with_children"
  is not set.
- Fix "old_fw" variable is used to indicate the reversed meaning.

- Link to v2: https://lore.kernel.org/r/20240506-dev-mule-i2c-mux-v2-0-a91c954f65d7@cherry.de

Changes in v2:
- Add i2c-adapter quirks to skip checking for conflict between the mux core
  and a child device address.
- Rename dt-binding to "tsd,mule-i2c-mux.yaml"
- Add Mule description to kconfig
- Fix indentation
- Move device table after probe

- Link to v1: https://lore.kernel.org/r/20240426-dev-mule-i2c-mux-v1-0-045a482f6ffb@theobroma-systems.com

---
Farouk Bouabid (7):
      i2c: mux: add the ability to share mux address with child nodes
      dt-bindings: i2c: mux: mule: add dt-bindings for mule i2c multiplexer
      i2c: muxes: add support for mule i2c multiplexer
      arm64: dts: rockchip: add mule i2c mux (0x18) on rk3399-puma
      arm64: dts: rockchip: add mule i2c mux (0x18) on rk3588-tiger
      arm64: dts: rockchip: add mule i2c mux (0x18) on px30-ringneck
      arm64: dts: rockchip: add mule i2c mux (0x18) on rk3588-jaguar

 .../devicetree/bindings/i2c/tsd,mule-i2c-mux.yaml  |  80 +++++++++++
 arch/arm64/boot/dts/rockchip/px30-ringneck.dtsi    |  20 ++-
 arch/arm64/boot/dts/rockchip/rk3399-puma.dtsi      |  20 ++-
 arch/arm64/boot/dts/rockchip/rk3588-jaguar.dts     |  19 ++-
 arch/arm64/boot/dts/rockchip/rk3588-tiger.dtsi     |  19 ++-
 drivers/i2c/i2c-core-base.c                        |   6 +-
 drivers/i2c/i2c-mux.c                              |  48 ++++++-
 drivers/i2c/muxes/Kconfig                          |  18 +++
 drivers/i2c/muxes/Makefile                         |   1 +
 drivers/i2c/muxes/i2c-mux-mule.c                   | 157 +++++++++++++++++++++
 include/linux/i2c-mux.h                            |   1 +
 include/linux/i2c.h                                |   7 +
 12 files changed, 384 insertions(+), 12 deletions(-)
---
base-commit: 79c1f584335af42ce359ee3ff0f4e9cc324296ed
change-id: 20240404-dev-mule-i2c-mux-9103cde07021

Best regards,
-- 
Farouk Bouabid <farouk.bouabid@cherry.de>