From: Jakub Kicinski <kuba@kernel.org>
Sent: Tuesday, June 13, 2023 1:45 AM

On Fri,  9 Jun 2023 14:18:46 +0200 Arkadiusz Kubalewski wrote:

quoted

+	xa_for_each(xa_pins, i, ref) {
+		if (ref->pin != pin)
+			continue;
+		reg = dpll_pin_registration_find(ref, ops, priv);
+		if (reg) {
+			refcount_inc(&ref->refcount);
+			return 0;
+		}
+		ref_exists = true;
+		break;
+	}
+
+	if (!ref_exists) {
+		ref = kzalloc(sizeof(*ref), GFP_KERNEL);
+		if (!ref)
+			return -ENOMEM;
+		ref->pin = pin;
+		INIT_LIST_HEAD(&ref->registration_list);
+		ret = xa_insert(xa_pins, pin->pin_idx, ref, GFP_KERNEL);
+		if (ret) {
+			kfree(ref);
+			return ret;
+		}
+		refcount_set(&ref->refcount, 1);
+	}
+
+	reg = kzalloc(sizeof(*reg), GFP_KERNEL);

Why do we have two structures - ref and reg?

Thank to Jiri and reg struct we solved a pin/dpll association
with multiple device drivers..
I.e. for pin:

struct dpll_pin_registration {
	struct list_head list;
	const struct dpll_pin_ops *ops;
	void *priv;
};

struct dpll_pin_ref {
	union {
		struct dpll_device *dpll;
		struct dpll_pin *pin;
	};
	struct list_head registration_list;
	refcount_t refcount;
};

struct dpll_pin {
	u32 id;
	u32 pin_idx;
	u64 clock_id;
	struct module *module;
	struct xarray dpll_refs;
	struct xarray parent_refs;
	const struct dpll_pin_properties *prop;
	char *rclk_dev_name;
	refcount_t refcount;
};

Basically, a pin or a device can be registered from multiple drivers,
where each driver has own priv and ops.
A single dpll_pin has references to dplls or pins (dpll_refs/parent_refs)
it is connected with, and thanks to registration list single reference can
have multiple drivers being attached with a particular dpll/pin.

The same scheme is for a dpll_device struct and associated pins.

quoted

+	if (!reg) {
+		if (!ref_exists)
+			kfree(ref);

ref has already been inserted into xa_pins

True, seems like a bug, will fix it.

Thank you,
Arkadiusz

quoted

+		return -ENOMEM;