[PATCH v4] i2c: cadence: Add shutdown handler

[Pandey, Radhey Shyam]

> During system reboot or kexec, in-flight I2C transfers can cause
> spurious interrupts or leave the bus in an undefined state. Add a
> shutdown handler that marks the adapter suspended and resets the
> controller, ensuring a clean handoff.
> 
> Signed-off-by: Ajay Neeli <ajay.neeli at amd.com>

Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey at amd.com>
Thanks!

> ---
> Link: https://lore.kernel.org/linux-i2c/20250730122907.18909-1-ajay.neeli@amd.com/
> 
> Changes v3->v4:
> - Replaced disable_irq() with cdns_i2c_master_reset() to avoid
>    potential deadlocks during shutdown
> - Added pm_runtime_status_suspended() check to skip register access
>    when clocks are disabled
> 
> Changes v2->v3:
> Corrected a typo that caused a build error in v2
> 
> Changes in v1->v2:
> Disable interrupts
> ---
>   drivers/i2c/busses/i2c-cadence.c | 20 ++++++++++++++++++++
>   1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-cadence.c b/drivers/i2c/busses/i2c-cadence.c
> index 0fb728ade92e..da8770182a18 100644
> --- a/drivers/i2c/busses/i2c-cadence.c
> +++ b/drivers/i2c/busses/i2c-cadence.c
> @@ -1635,6 +1635,25 @@ static void cdns_i2c_remove(struct platform_device *pdev)
>   	reset_control_assert(id->reset);
>   }
>   
> +/**
> + * cdns_i2c_shutdown - Prepare I2C controller for system shutdown
> + * @pdev:	Handle to the platform device structure
> + *
> + * Mark the adapter as suspended and reset the controller to ensure a clean
> + * handoff during system reboot or kexec.
> + */
> +static void cdns_i2c_shutdown(struct platform_device *pdev)
> +{
> +	struct cdns_i2c *id = platform_get_drvdata(pdev);
> +
> +	/* Mark the adapter as suspended to prevent further I2C transfers */
> +	i2c_mark_adapter_suspended(&id->adap);
> +
> +	/* Reset the controller state if active - clocks are disabled when suspended */
> +	if (!pm_runtime_status_suspended(&pdev->dev))
> +		cdns_i2c_master_reset(&id->adap);
> +}
> +
>   static struct platform_driver cdns_i2c_drv = {
>   	.driver = {
>   		.name  = DRIVER_NAME,
> @@ -1643,6 +1662,7 @@ static struct platform_driver cdns_i2c_drv = {
>   	},
>   	.probe  = cdns_i2c_probe,
>   	.remove = cdns_i2c_remove,
> +	.shutdown = cdns_i2c_shutdown,
>   };
>   
>   module_platform_driver(cdns_i2c_drv);