Re: [PATCH RFC net-next 06/13] dpll: Support dynamic pin index allocation

[Przemek Kitszel <przemyslaw.kitszel@intel.com>]

On 12/11/25 20:47, Ivan Vecera wrote:
> Allow drivers to register DPLL pins without manually specifying a pin
> index.
> 
> Currently, drivers must provide a unique pin index when calling
> dpll_pin_get(). This works well for hardware-mapped pins but creates
> friction for drivers handling virtual pins or those without a strict
> hardware indexing scheme.

wouldn't it be better to just switch everything to allocated IDs?

> 
> Introduce DPLL_PIN_IDX_UNSPEC (U32_MAX). When a driver passes this
> value as the pin index:
> 1. The core allocates a unique index using an IDA
> 2. The allocated index is mapped to a range starting above `INT_MAX`
> 
> This separation ensures that dynamically allocated indices never collide
> with standard driver-provided hardware indices, which are assumed to be
> within the `0` to `INT_MAX` range. The index is automatically freed when
> the pin is released in dpll_pin_put().
> 
> Signed-off-by: Ivan Vecera <ivecera@redhat.com>
> ---
>   drivers/dpll/dpll_core.c | 48 ++++++++++++++++++++++++++++++++++++++--
>   include/linux/dpll.h     |  2 ++
>   2 files changed, 48 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dpll/dpll_core.c b/drivers/dpll/dpll_core.c
> index fecc3d97acf5b..79f60e0de27ac 100644
> --- a/drivers/dpll/dpll_core.c
> +++ b/drivers/dpll/dpll_core.c
> @@ -10,6 +10,7 @@
>   
>   #include <linux/device.h>
>   #include <linux/err.h>
> +#include <linux/idr.h>
>   #include <linux/property.h>
>   #include <linux/slab.h>
>   #include <linux/string.h>
> @@ -24,6 +25,7 @@ DEFINE_XARRAY_FLAGS(dpll_device_xa, XA_FLAGS_ALLOC);
>   DEFINE_XARRAY_FLAGS(dpll_pin_xa, XA_FLAGS_ALLOC);
>   
>   static RAW_NOTIFIER_HEAD(dpll_notifier_chain);
> +static DEFINE_IDA(dpll_pin_idx_ida);
>   
>   static u32 dpll_device_xa_id;
>   static u32 dpll_pin_xa_id;
> @@ -468,6 +470,36 @@ void dpll_device_unregister(struct dpll_device *dpll,
>   }
>   EXPORT_SYMBOL_GPL(dpll_device_unregister);
>   
> +static int dpll_pin_idx_alloc(u32 *pin_idx)
> +{
> +	int ret;
> +
> +	if (!pin_idx)
> +		return -EINVAL;
> +
> +	/* Alloc unique number from IDA. Number belongs to <0, INT_MAX> range */
> +	ret = ida_alloc(&dpll_pin_idx_ida, GFP_KERNEL);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Map the value to dynamic pin index range <INT_MAX+1, U32_MAX> */
> +	*pin_idx = (u32)ret + INT_MAX + 1;
> +
> +	return 0;
> +}
> +
> +static void dpll_pin_idx_free(u32 pin_idx)
> +{
> +	if (pin_idx <= INT_MAX)
> +		return; /* Not a dynamic pin index */
> +
> +	/* Map the index value from dynamic pin index range to IDA range and
> +	 * free it.
> +	 */
> +	pin_idx -= INT_MAX - 1;
> +	ida_free(&dpll_pin_idx_ida, pin_idx);
> +}
> +
>   static void dpll_pin_prop_free(struct dpll_pin_properties *prop)
>   {
>   	kfree(prop->package_label);
> @@ -526,9 +558,18 @@ dpll_pin_alloc(u64 clock_id, u32 pin_idx, struct module *module,
>   	struct dpll_pin *pin;
>   	int ret;
>   
> +	if (pin_idx == DPLL_PIN_IDX_UNSPEC) {
> +		ret = dpll_pin_idx_alloc(&pin_idx);
> +		if (ret)
> +			return ERR_PTR(ret);
> +	} else if (pin_idx > INT_MAX) {
> +		return ERR_PTR(-EINVAL);
> +	}
>   	pin = kzalloc(sizeof(*pin), GFP_KERNEL);
> -	if (!pin)
> -		return ERR_PTR(-ENOMEM);
> +	if (!pin) {
> +		ret = -ENOMEM;
> +		goto err_pin_alloc;
> +	}
>   	pin->pin_idx = pin_idx;
>   	pin->clock_id = clock_id;
>   	pin->module = module;
> @@ -557,6 +598,8 @@ dpll_pin_alloc(u64 clock_id, u32 pin_idx, struct module *module,
>   	dpll_pin_prop_free(&pin->prop);
>   err_pin_prop:
>   	kfree(pin);
> +err_pin_alloc:
> +	dpll_pin_idx_free(pin_idx);
>   	return ERR_PTR(ret);
>   }
>   
> @@ -663,6 +706,7 @@ void dpll_pin_put(struct dpll_pin *pin)
>   		xa_destroy(&pin->ref_sync_pins);
>   		dpll_pin_prop_free(&pin->prop);
>   		fwnode_handle_put(pin->fwnode);
> +		dpll_pin_idx_free(pin->pin_idx);
>   		kfree_rcu(pin, rcu);
>   	}
>   	mutex_unlock(&dpll_lock);
> diff --git a/include/linux/dpll.h b/include/linux/dpll.h
> index 441afb90d2a29..8aa1df38ce563 100644
> --- a/include/linux/dpll.h
> +++ b/include/linux/dpll.h
> @@ -235,6 +235,8 @@ int dpll_device_register(struct dpll_device *dpll, enum dpll_type type,
>   void dpll_device_unregister(struct dpll_device *dpll,
>   			    const struct dpll_device_ops *ops, void *priv);
>   
> +#define DPLL_PIN_IDX_UNSPEC	U32_MAX
> +
>   struct dpll_pin *
>   dpll_pin_get(u64 clock_id, u32 dev_driver_id, struct module *module,
>   	     const struct dpll_pin_properties *prop,