[PATCH v7 0/2] i2c: Add dynamic transfer timeout based on message length and frequency

The I2C core and many controller drivers currently rely on a fixed
timeout value that does not account for transfer characteristics such as
message length or bus frequency. This can make the timeout unnecessarily
large for short transfers, while longer transfers at lower bus
frequencies may require a timeout that better matches the expected
transfer duration.

Introduce a generic helper API in the I2C core to calculate a
transfer-specific timeout from the expected wire time of a transaction.
Store the computed value in adap->timeout so that both the I2C core retry
logic and controller drivers use a timeout value that reflects the
current transfer.

Keep timeout policy decisions within individual controller drivers. Let
drivers provide their own safety margins and minimum timeout floors, and
avoid exposing those driver-specific policy values as part of the
generic API.

Convert the Qualcomm GENI I2C driver to use the helper while preserving
its existing timeout policy. Preserve the static timeout behaviour when
CONFIG_I2C_DYNAMIC_TIMEOUT is disabled, and let a userspace-configured
I2C_TIMEOUT value take precedence over the computed timeout.

Suggested-by: Dmitry Guzman <[email protected]>

Changes in v7:
- Add CONFIG_I2C_DYNAMIC_TIMEOUT to gate i2c_update_timeout(); no-op
  stub when config is disabled preserving existing static behaviour
- Store userspace I2C_TIMEOUT ioctl value in a new adap->user_timeout
  field; userspace-configured timeout always takes precedence over the
  kernel-computed value
- Fix geni_i2c_gpi_multi_xfer_timeout_handler() parameter type u32 ->
  unsigned long to match wait_for_completion_timeout() expectation

Changes in v6:
- Split into two patches: core helper + driver consumer
- Moved timeout calculation to i2c-core as i2c_update_timeout(), which
  writes directly into adap->timeout so all consumers of that field
  (including the __i2c_transfer() retry loop) benefit automatically
- Driver supplies safety coefficient and minimum floor as parameters,
  keeping I2C_TIMEOUT_SAFETY_COEFFICIENT and I2C_TIMEOUT_MIN_USEC
  internal to i2c-qcom-geni.c
- Compute timeout once per batch in geni_i2c_xfer() using max message
  length, all internal wait sites read adap->timeout directly

Link: https://lore.kernel.org/r/[email protected]

Signed-off-by: Aniket Randive <[email protected]>
---
Aniket Randive (2):
      i2c: core: Add i2c_update_timeout() helper for dynamic transfer timeouts
      i2c: qcom-geni: Add dynamic transfer timeout based on transfer length and frequency

 drivers/i2c/Kconfig                | 13 +++++++++++
 drivers/i2c/busses/i2c-qcom-geni.c | 44 ++++++++++++++++++++++++++++++--------
 drivers/i2c/i2c-core-base.c        | 40 ++++++++++++++++++++++++++++++++++
 drivers/i2c/i2c-dev.c              |  4 ++++
 include/linux/i2c.h                | 12 +++++++++++
 5 files changed, 104 insertions(+), 9 deletions(-)
---
base-commit: 3d08ff75a47a3e7e2ab45a3bcab6723b4d906422
change-id: 20260716-master-f7da57c7529a

Best regards,
--  
Aniket Randive <[email protected]>