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

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

On 5/8/25 11:30 AM, EnDe Tan wrote:
> Hi Andi and Jarkko, thank you for the feedback.
> 
>> -----Original Message-----
>> From: Andi Shyti <andi.shyti@kernel.org>
>> Sent: Tuesday, 6 May, 2025 5:49 AM
>> To: Jarkko Nikula <jarkko.nikula@linux.intel.com>
>> Cc: EnDe Tan <ende.tan@starfivetech.com>; linux-i2c@vger.kernel.org;
> ...
>>> Good explanation and could you add it the commit log together with the
>>> example?
>>
>> If you want you can paste the new commit log as reply to this e-mail.
> 
> Here is the new commit log, feel free to let me know if further changes are required:
> 
> 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
> ```
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>