[PATCH 0/2] i2c: qcom-cci: Recover after a target powers down under a running controller

[Birk Skyum]

On the Lenovo Yoga Slim 7x (X1E80100) the OV02C10 front camera on CCI1
master 1 fails to start whenever it is opened again within about a
second of being closed. The first register write times out ("master 1
queue 0 timeout") and the stream does not start. Two attempts so far
treated this as a sensor power-up problem. One gave the ov02c10 driver a
longer settle time, the other a minimum off time for the camera rails
through regulator-off-on-delay-us [1]. Neither is needed.

The sensor holds SCL and SDA low while it is powered down. If the CCI
controller stays clocked from then until its next transfer, the master
no longer starts transfers. The queue stays on its first command, no
interrupt arrives, and only the reset in cci_run_queue()'s timeout path
brings it back. A runtime suspend clears the state too, but only when
the power domain collapses, because cci_resume_runtime() does not reset
the controller. With the 1 s autosuspend delay, any power cycle of a
target that is shorter than a second runs into it.

Patch 1 resets the controller on every runtime resume. Patch 2 suspends
it 50 ms after its last transfer.

Tested on the Yoga with the driver from i2c/i2c-next, built as a module
for a 7.2.8-based kernel whose device tree has no off-on delay for the
camera rails. The CCI clock runs at 37.5 MHz there. Starting the camera
with v4l2-ctl after a pause:

  pause          0.05 s  0.1 s  0.2 s  0.5 s  1 s
  failed before   19/20  19/20  19/20  19/20  16/20
  failed after     0/20   0/20   0/20   0/20   0/20

With the series, 150 libcamera starts back to back all started, so the
sensor itself starts fine after a 50 ms pause. The same two changes on
7.2.8's driver, with the CCI clock at 19.2 MHz, gave the same result.

[1] https://lore.kernel.org/all/20261001-regulator-off-on-delay-v4-0-258ba9612da8@xxxxxxxxxxxxxxxx/

Birk Skyum (2):
  i2c: qcom-cci: Reset the controller when it resumes
  i2c: qcom-cci: Suspend the controller 50 ms after the last transfer

 drivers/i2c/busses/i2c-qcom-cci.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

base-commit: bd4a545e4f5dbd5e4dd0064777429813516b8784
-- 
2.53.0