Re: [1/1] i2c: designware: Ensure runtime suspend is invoked during rapid slave unregistration and registration

[Jarkko Nikula <jarkko.nikula@linux.intel.com>]

Hi

Sorry the delay. Comment below.

On 4/20/25 6:31 AM, EnDe Tan wrote:
> It appears that when performing a rapid sequence of `delete_device -> new_device -> delete_device -> new_device`, the `dw_i2c_plat_runtime_suspend` is not invoked for the second `delete_device`.
> 
> This seems to happen because when `i2c_dw_unreg_slave` is about to trigger suspend during the second `delete_device`, the second `new_device` operation cancels the suspend. As a result, `dw_i2c_plat_runtime_resume` is not called (since there was no suspend), which means `i_dev->init` (i.e., `i2c_dw_init_slave`) is skipped.
> 
> Because `i2c_dw_init_slave` is skipped, `i2c_dw_configure_fifo_slave` is not invoked, which leaves `DW_IC_INTR_MASK` unconfigured.
> If we inspect the interrupt mask register using devmem, it will show as zero.
> 
> Here's an 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
> 
> # If we use devmem to inspect IC_INTR_MASK, it will show as zero
> ```
> 
Good explanation and could you add it the commit log together with the 
example?