linux-kernel - [PATCH v5 0/6] i2c: designware: Improve support of multi-messages transfer

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Message-Id: <20260120-i2c-dw-v5-0-0e34d6d9455c@bootlin.com>
Date: Tue, 20 Jan 2026 10:28:00 +0100
From: Benoît Monin <benoit.monin@...tlin.com>
To: Andi Shyti <andi.shyti@...nel.org>, 
 Mika Westerberg <mika.westerberg@...ux.intel.com>, 
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
 Jan Dabros <jsd@...ihalf.com>, 
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
 Clark Williams <clrkwllms@...nel.org>, Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 Gregory CLEMENT <gregory.clement@...tlin.com>, 
 Théo Lebrun <theo.lebrun@...tlin.com>, 
 Tawfik Bayouk <tawfik.bayouk@...ileye.com>, 
 Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>, 
 Dmitry Guzman <dmitry.guzman@...ileye.com>, linux-i2c@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev, 
 Benoît Monin <benoit.monin@...tlin.com>
Subject: [PATCH v5 0/6] i2c: designware: Improve support of multi-messages
 transfer

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@...tlin.com>
---
Changes in v5:
- Rebased on v6.19-rc6 and fully retested on EyeQ6Lplus.
- Drop dt-binding patch: already merged upstream in v6.19-rc2.
- From Andi Shyti's review:
  - __i2c_dw_xfer_one_part() now returns 0 on success instead
    of the number of messages transferred.
  - Drop inline keyword from i2c_dw_msg_is_valid() declaration.
- Link to v4: https://lore.kernel.org/r/20251126-i2c-dw-v4-0-b0654598e7c5@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 (6):
      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

 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 +-
 4 files changed, 153 insertions(+), 58 deletions(-)
---
base-commit: 24d479d26b25bce5faea3ddd9fa8f3a6c3129ea7
change-id: 20251014-i2c-dw-da315f758296

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