[PATCH v2 0/5] i2c: designware: Improve support of multi-messages transfer

["Benoît Monin" <benoit.monin@bootlin.com>]

Add support for the I2C_M_STOP flag to the .xfer() function of the
designware driver. This allows grouping multiple accesses in a single
call and changing the target address after a STOP flag. This is achieved
by splitting i2c_dw_xfer() in two functions. The core logic handling
the transaction is now in __i2c_dw_xfer_unlocked(), while i2c_dw_xfer()
loops over the messages to search for the I2C_M_STOP flag and calls
__i2c_dw_xfer_unlocked().

Handle controllers that lack the ability to emit a RESTART when two
consecutive messages have the same address and direction by aborting
transfers that contain such a sequence of messages. For those controllers,
we also check that we do not get any unwanted STOP caused by a Tx FIFO
underrun, as they lack the ability to hold the clock during a transaction.

The I2C controllers found in the EyeQ6Lplus and EyeQ7H SoCs from Mobileye
lack such capability, so a compatible string is added because this cannot
be detected at runtime.

This patch series also brings two cleanups. One in i2c_dw_read() optimizes
the read of the message flags. And the other sorts the compatible strings
alphabetically in dw_i2c_of_match[].

Signed-off-by: Benoît Monin <benoit.monin@bootlin.com>
---
Changes in v2:
- Add a single compatible for mobileye i2c controllers based in
  DesignWare IP.
- Handle the I2C_M_STOP flag instead of emiting a STOP on target address
  change.
- Abort transfer when it requires a RESTART on controller that cannot
  emit them.
- Detect FIFO underrun instead of disabling threaded interrupt on
  PREEMPT_RT kernel.
- Sort the compatible entries in a separate patch.
- Add a cleanup patch on flag reading in i2c_dw_read().
- Link to v1: https://lore.kernel.org/r/20251017-i2c-dw-v1-0-7b85b71c7a87@bootlin.com

---
Benoît Monin (5):
      dt-bindings: i2c: dw: Add Mobileye I2C controllers
      i2c: designware: Optimize flag reading in i2c_dw_read()
      i2c: designware: Sort compatible strings in alphabetical order
      i2c: designware: Implement I2C_M_STOP support
      i2c: designware: Support of controller with IC_EMPTYFIFO_HOLD_MASTER disabled

 .../bindings/i2c/snps,designware-i2c.yaml          |   1 +
 drivers/i2c/busses/i2c-designware-core.h           |   1 +
 drivers/i2c/busses/i2c-designware-master.c         | 159 ++++++++++++++++-----
 drivers/i2c/busses/i2c-designware-platdrv.c        |   5 +-
 4 files changed, 128 insertions(+), 38 deletions(-)
---
base-commit: dcb6fa37fd7bc9c3d2b066329b0d27dedf8becaa
change-id: 20251014-i2c-dw-da315f758296

Best regards,
-- 
Benoît Monin, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com