i2c: designware: Invoke runtime suspend on quick slave re-registration

Replaced pm_runtime_put() with pm_runtime_put_sync_suspend() to ensure
the runtime suspend is invoked immediately when unregistering a slave.
This prevents a race condition where suspend was skipped when
unregistering and registering slave in quick succession.

For example, consider the rapid sequence of
`delete_device -> new_device -> delete_device -> new_device`.
In this sequence, it is observed that the dw_i2c_plat_runtime_suspend()
might not be invoked after `delete_device` operation.

This is because after `delete_device` operation, when the
pm_runtime_put() is about to trigger suspend, the following `new_device`
operation might race and cancel the suspend.

If that happens, during the `new_device` operation,
dw_i2c_plat_runtime_resume() is skipped (since there was no suspend), which
means `i_dev->init()`, i.e. i2c_dw_init_slave(), is skipped.
Since i2c_dw_init_slave() is skipped, i2c_dw_configure_fifo_slave() is
skipped too, which leaves `DW_IC_INTR_MASK` unconfigured. If we inspect
the interrupt mask register using devmem, it will show as zero.

Example shell script to reproduce the issue:
```
  #!/bin/sh

  SLAVE_LADDR=0x1010
  SLAVE_BUS=13
  NEW_DEVICE=/sys/bus/i2c/devices/i2c-$SLAVE_BUS/new_device
  DELETE_DEVICE=/sys/bus/i2c/devices/i2c-$SLAVE_BUS/delete_device

  # Create initial device
  echo slave-24c02 $SLAVE_LADDR > $NEW_DEVICE
  sleep 2

  # Rapid sequence of
  # delete_device -> new_device -> delete_device -> new_device
  echo $SLAVE_LADDR > $DELETE_DEVICE
  echo slave-24c02 $SLAVE_LADDR > $NEW_DEVICE
  echo $SLAVE_LADDR > $DELETE_DEVICE
  echo slave-24c02 $SLAVE_LADDR > $NEW_DEVICE

  # Using devmem to inspect IC_INTR_MASK will show as zero
```

Signed-off-by: Tan En De <ende.tan@starfivetech.com>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Link: https://lore.kernel.org/r/20250412023303.378600-1-ende.tan@starfivetech.com
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>

diff --git a/drivers/i2c/busses/i2c-designware-slave.c b/drivers/i2c/busses/i2c-designware-slave.c
index 5cd4a5f7a472e4220d33f0d0ac375f3c0189f741..b936a240db0a9308f005148cdf4c4f9fd512be05 100644 (file)
--- a/drivers/i2c/busses/i2c-designware-slave.c
+++ b/drivers/i2c/busses/i2c-designware-slave.c
@@ -96,7 +96,7 @@ static int i2c_dw_unreg_slave(struct i2c_client *slave)
        i2c_dw_disable(dev);
        synchronize_irq(dev->irq);
        dev->slave = NULL;
-       pm_runtime_put(dev->dev);
+       pm_runtime_put_sync_suspend(dev->dev);
 
        return 0;
 }