linux-kernel - RE: [RFC PATCH v8 03/10] dpll: core: Add DPLL framework base functions

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Message-ID: <DM6PR11MB4657FED589F5922BBAC5D9059B5DA@DM6PR11MB4657.namprd11.prod.outlook.com>
Date:   Wed, 21 Jun 2023 21:17:26 +0000
From:   "Kubalewski, Arkadiusz" <arkadiusz.kubalewski@...el.com>
To:     Jakub Kicinski <kuba@...nel.org>
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Subject: RE: [RFC PATCH v8 03/10] dpll: core: Add DPLL framework base
 functions

>From: Jakub Kicinski <kuba@...nel.org>
>Sent: Tuesday, June 13, 2023 1:45 AM
>
>On Fri,  9 Jun 2023 14:18:46 +0200 Arkadiusz Kubalewski wrote:
>> +	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.


>> +	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

>> +		return -ENOMEM;