Re: [PATCH] spi: Add spi_for_each_controller() helper

[Mark Brown <broonie@kernel.org>]

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On Thu, May 14, 2026 at 04:45:44PM +0800, ChaoHuang wrote:
> From: Chao Huang <huangchao@kylinos.cn>
> 
> Add a new helper function to iterate over all SPI controllers.
> This provides a convenient way for SPI core code and drivers
> to perform operations on all registered controllers.

> This helper is useful for scenarios like statistics gathering,
> configuration updates, or debugging operations that need to
> process all SPI controllers in the system.

Do you have an actual user for this or is this just purely theoretical
at this point?  It'd make a lot more sense to add this along with a
user.

> +int spi_for_each_controller(int (*fn)(struct spi_controller *, void *), void *data)
> +{
> +	struct spi_controller *ctlr;
> +	int ret = 0;
> +
> +	mutex_lock(&board_lock);
> +	list_for_each_entry(ctlr, &spi_controller_list, list) {
> +		ret = fn(ctlr, data);

When unregistering controllers we do start the teardown process before
we pull the device off the controller list, and drop the lock while
doing so.  That's probably fine for a lot of uses.

There's also some obvious potential for things to go wrong here with
something in the callback deadlocking, though that's a bit of a "don't
do that kind of thing".

> +		if (ret)
> +			break;
> +	}
> +	mutex_unlock(&board_lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(spi_for_each_controller);
> +
>  static int __init spi_init(void)
>  {
>  	int	status;
> diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
> index 79513f5941cc..8fcf3faf9739 100644
> --- a/include/linux/spi/spi.h
> +++ b/include/linux/spi/spi.h
> @@ -934,6 +934,8 @@ static inline int acpi_spi_count_resources(struct acpi_device *adev)
>  }
>  #endif
>  
> +int spi_for_each_controller(int (*fn)(struct spi_controller *, void *), void *data);
> +
>  /*
>   * SPI resource management while processing a SPI message
>   */
> -- 
> 2.25.1
> 

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