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_one_part(), while i2c_dw_xfer()
loops over the messages to search for the I2C_M_STOP flag and calls
__i2c_dw_xfer_one_part().

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.
And we set the irq as non-threaded to prevent underrun on PREEMPT-RT
kernel when filling the FIFO.

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 four cleanups:
* Optimize the read of the message flags in i2c_dw_read().
* Sort the compatible strings alphabetically in dw_i2c_of_match[].
* Simplify runtime PM handling in i2c_dw_xfer() with guard.
* Add a dedicated i2c_algorithm for AMD NAVI controller.

Signed-off-by: Benoît Monin <benoit.monin@bootlin.com>
---
Changes in v4:
- Use a boolean property instead of a flag for handling controllers
  IC_EMPTYFIFO_HOLD_MASTER_EN.
- Reorder the patches so goto and runtime PM auto-cleanup are not mixed
  in i2c_dw_xfer().
- Drop goto in __i2c_dw_xfer_one_part() and use return.
- Tidy up comments for i2c_dw_msg_is_valid() and irq_flags.
- Link to v3: https://lore.kernel.org/r/20251119-i2c-dw-v3-0-bc4bc2a2cbac@bootlin.com

Changes in v3:
- Add a compatible entry for Mobileye EyeQ7H i2c controllers.
- Use runtime PM macro for auto-cleanup in i2c_dw_xfer().
- Add a dedicated i2c_algorithm for AMD NAVI controllers.
- Rename __i2c_dw_xfer_unlocked() as it is not about locking at all.
- Rework the validity check of i2c_msg.
- Flag the irq as non-threaded for controllers that cannot hold the
  clock to avoid underrun.
- Link to v2: https://lore.kernel.org/r/20251031-i2c-dw-v2-0-90416874fcc0@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 emitting 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 (7):
      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: Add dedicated algorithm for AMD NAVI
      i2c: designware: Implement I2C_M_STOP support
      i2c: designware: Use runtime PM macro for auto-cleanup
      i2c: designware: Support of controller with IC_EMPTYFIFO_HOLD_MASTER disabled

 .../bindings/i2c/snps,designware-i2c.yaml          |   7 +
 drivers/i2c/busses/i2c-designware-common.c         |   6 +
 drivers/i2c/busses/i2c-designware-core.h           |   3 +
 drivers/i2c/busses/i2c-designware-master.c         | 197 +++++++++++++++------
 drivers/i2c/busses/i2c-designware-platdrv.c        |   5 +-
 5 files changed, 160 insertions(+), 58 deletions(-)
---
base-commit: 6772718099e29703ed50dcd0941a135d1fb6e612
change-id: 20251014-i2c-dw-da315f758296

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

Hi,

On Wed, Nov 26, 2025 at 11:46:23AM +0100, Benoît Monin wrote:
> 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_one_part(), while i2c_dw_xfer()
> loops over the messages to search for the I2C_M_STOP flag and calls
> __i2c_dw_xfer_one_part().
> 
> 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.
> And we set the irq as non-threaded to prevent underrun on PREEMPT-RT
> kernel when filling the FIFO.
> 
> 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 four cleanups:
> * Optimize the read of the message flags in i2c_dw_read().
> * Sort the compatible strings alphabetically in dw_i2c_of_match[].
> * Simplify runtime PM handling in i2c_dw_xfer() with guard.
> * Add a dedicated i2c_algorithm for AMD NAVI controller.
> 
> Signed-off-by: Benoît Monin <benoit.monin@bootlin.com>

All look good to me now, thanks! I also checked that this did not break
anything -> my laptop I2C connected touchscreen & touchpad still works.

For the series,

Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>