Re: [PATCH v3 07/12] reset: Add reset_control_get_from_provider_exclusive()

[Philipp Zabel <p.zabel@pengutronix.de>]

On Mi, 2026-09-02 at 13:29 +0200, Geert Uytterhoeven wrote:
> When stacking two reset controllers, the upper one should go through the
> proper channels: request exclusive reset controls and use them via the
> reset_control_*() APIs.  However, unlike the clock subsystem, which has
> of_clk_get_from_provider(), the reset subsystem does not offer a way to
> lookup and obtain a reset from a reset provider.
> 
> Hence add a public helper reset_control_get_from_provider_exclusive()
> to lookup and obtain an exclusive reference to a reset controller, based
> on the recently introduced __reset_control_get_from_provider() helper.
> This will be used by the R-Car X5H Module Controller driver.
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
> v3:
>   - Replace reset_controller_get_provider() by
>     reset_control_get_from_provider_exclusive(),
>   - Add kerneldoc,
> 
> v2:
>   - No changes.
> ---
>  drivers/reset/core.c  | 37 ++++++++++++++++++++++++++++++++-----
>  include/linux/reset.h |  8 ++++++++
>  2 files changed, 40 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/reset/core.c b/drivers/reset/core.c
> index 8af7cd2e8a5029df..6d4c95b3edb18248 100644
> --- a/drivers/reset/core.c
> +++ b/drivers/reset/core.c
> @@ -1141,6 +1141,7 @@ __reset_control_get_from_provider(const struct fwnode_reference_args *args,
>  				  bool gpio_fallback,
>  				  enum reset_control_flags flags)
>  {
> +	struct fwnode_handle *fwnode = consumer ?: args->fwnode;
>  	struct reset_control *rstc = ERR_PTR(-EINVAL);
>  	struct reset_controller_dev *rcdev;
>  	int rstc_id = -EINVAL;
> @@ -1154,18 +1155,26 @@ __reset_control_get_from_provider(const struct fwnode_reference_args *args,
>  	if (WARN_ON(args->nargs != rcdev->fwnode_reset_n_cells))
>  		return ERR_PTR(-EINVAL);
>  
> -	if (rcdev->of_xlate && is_of_node(consumer)) {
> -		struct device_node *np = to_of_node(consumer);
> +	if (rcdev->of_xlate && is_of_node(fwnode)) {
> +		struct device_node *np = to_of_node(fwnode);
>  		struct of_phandle_args of_args;
>  		int ret;
>  
> -		ret = of_parse_phandle_with_args(np,
> +		if (consumer) {
> +			ret = of_parse_phandle_with_args(np,
>  					 gpio_fallback ? "reset-gpios" : "resets",
>  					 gpio_fallback ? "#gpio-cells" : "#reset-cells",
>  					 gpio_fallback ? 0 : index,
>  					 &of_args);
> -		if (ret)
> -			return ERR_PTR(ret);
> +			if (ret)
> +				return ERR_PTR(ret);
> +		} else {
> +			of_args.np = of_node_get(np);
> +			of_args.args_count = args->nargs;
> +
> +			for (unsigned int i = 0; i < args->nargs; i++)
> +				of_args.args[i] = args->args[i];

This should error out if args->args[i] > U32_MAX.

> +		}
>  
>  		rstc_id = rcdev->of_xlate(rcdev, &of_args);
>  		of_node_put(of_args.np);
> @@ -1257,6 +1266,24 @@ struct reset_control *__reset_control_get(struct device *dev, const char *id,
>  }
>  EXPORT_SYMBOL_GPL(__reset_control_get);
>  
> +/**
> + * reset_control_get_from_provider_exclusive - Lookup and obtain an exclusive
> + *					       reference to a reset controller.
> + * @args: Reference to the reset controller provider with all the args like
> + *	  reset number

It is implied, but should this explicitly mention that this must not be
a reference to a GPIO provider?

> + *
> + * Returns a struct reset_control or IS_ERR() condition containing errno.
> + * If this function is called more than once for the same reset control it will
> + * return -EBUSY.
> + */
> +struct reset_control *
> +reset_control_get_from_provider_exclusive(const struct fwnode_reference_args *args)
> +{
> +	return __reset_control_get_from_provider(args, NULL, 0, false,
> +						 RESET_CONTROL_EXCLUSIVE);
> +}
> +EXPORT_SYMBOL_GPL(reset_control_get_from_provider_exclusive);

regards
Philipp