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From:   Cristian Marussi <cristian.marussi@arm.com>
To:     linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Cc:     sudeep.holla@arm.com, lukasz.luba@arm.com,
        james.quinlan@broadcom.com, Jonathan.Cameron@Huawei.com,
        f.fainelli@gmail.com, etienne.carriere@linaro.org,
        thara.gopinath@linaro.org, vincent.guittot@linaro.org,
        souvik.chakravarty@arm.com, cristian.marussi@arm.com
Subject: [PATCH 03/11] firmware: arm_scmi: introduce common protocol interface
Date:   Wed, 14 Oct 2020 16:05:37 +0100
Message-Id: <20201014150545.44807-4-cristian.marussi@arm.com>
In-Reply-To: <20201014150545.44807-1-cristian.marussi@arm.com>
References: <20201014150545.44807-1-cristian.marussi@arm.com>
Precedence: bulk

Introduce generic get_ops/put_ops handle operations: any protocol, both
standard or custom, now exposes its operations through this common
interface which internally takes care to account for protocols' usage:
protocols' initialization is now performed on demand as soon as the first
user shows up while deinitialization (if any) is performed once
the last user of a protocol has gone.
Registered events' notifier are tracked too against the related protocol.
Convert all SCMI drivers to the new interface too.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
 drivers/clk/clk-scmi.c                     | 30 +++++++++----
 drivers/cpufreq/scmi-cpufreq.c             | 28 ++++++------
 drivers/firmware/arm_scmi/base.c           |  2 +-
 drivers/firmware/arm_scmi/bus.c            | 24 -----------
 drivers/firmware/arm_scmi/clock.c          |  4 +-
 drivers/firmware/arm_scmi/common.h         |  6 +--
 drivers/firmware/arm_scmi/driver.c         | 31 ++++++++++++--
 drivers/firmware/arm_scmi/notify.c         | 50 +++++++++++++++++++---
 drivers/firmware/arm_scmi/perf.c           |  3 +-
 drivers/firmware/arm_scmi/power.c          |  3 +-
 drivers/firmware/arm_scmi/reset.c          |  3 +-
 drivers/firmware/arm_scmi/scmi_pm_domain.c | 29 +++++++++----
 drivers/firmware/arm_scmi/sensors.c        |  3 +-
 drivers/firmware/arm_scmi/system.c         |  2 +-
 drivers/hwmon/scmi-hwmon.c                 | 26 ++++++++---
 drivers/reset/reset-scmi.c                 | 26 ++++++++---
 include/linux/scmi_protocol.h              | 15 +++----
 17 files changed, 185 insertions(+), 100 deletions(-)

diff --git a/drivers/clk/clk-scmi.c b/drivers/clk/clk-scmi.c
index c754dfbb73fd..4801a2df044b 100644
--- a/drivers/clk/clk-scmi.c
+++ b/drivers/clk/clk-scmi.c
@@ -2,7 +2,7 @@
 /*
  * System Control and Power Interface (SCMI) Protocol based clock driver
  *
- * Copyright (C) 2018 ARM Ltd.
+ * Copyright (C) 2018-2020 ARM Ltd.
  */
 
 #include <linux/clk-provider.h>
@@ -13,6 +13,8 @@
 #include <linux/scmi_protocol.h>
 #include <asm/div64.h>
 
+static const struct scmi_clk_ops *clk_ops;
+
 struct scmi_clk {
 	u32 id;
 	struct clk_hw hw;
@@ -29,7 +31,7 @@ static unsigned long scmi_clk_recalc_rate(struct clk_hw *hw,
 	u64 rate;
 	struct scmi_clk *clk = to_scmi_clk(hw);
 
-	ret = clk->handle->clk_ops->rate_get(clk->handle, clk->id, &rate);
+	ret = clk_ops->rate_get(clk->handle, clk->id, &rate);
 	if (ret)
 		return 0;
 	return rate;
@@ -69,21 +71,21 @@ static int scmi_clk_set_rate(struct clk_hw *hw, unsigned long rate,
 {
 	struct scmi_clk *clk = to_scmi_clk(hw);
 
-	return clk->handle->clk_ops->rate_set(clk->handle, clk->id, rate);
+	return clk_ops->rate_set(clk->handle, clk->id, rate);
 }
 
 static int scmi_clk_enable(struct clk_hw *hw)
 {
 	struct scmi_clk *clk = to_scmi_clk(hw);
 
-	return clk->handle->clk_ops->enable(clk->handle, clk->id);
+	return clk_ops->enable(clk->handle, clk->id);
 }
 
 static void scmi_clk_disable(struct clk_hw *hw)
 {
 	struct scmi_clk *clk = to_scmi_clk(hw);
 
-	clk->handle->clk_ops->disable(clk->handle, clk->id);
+	clk_ops->disable(clk->handle, clk->id);
 }
 
 static const struct clk_ops scmi_clk_ops = {
@@ -143,10 +145,14 @@ static int scmi_clocks_probe(struct scmi_device *sdev)
 	struct device_node *np = dev->of_node;
 	const struct scmi_handle *handle = sdev->handle;
 
-	if (!handle || !handle->clk_ops)
+	if (!handle)
 		return -ENODEV;
 
-	count = handle->clk_ops->count_get(handle);
+	clk_ops = handle->get_ops(handle, SCMI_PROTOCOL_CLOCK);
+	if (IS_ERR(clk_ops))
+		return PTR_ERR(clk_ops);
+
+	count = clk_ops->count_get(handle);
 	if (count < 0) {
 		dev_err(dev, "%pOFn: invalid clock output count\n", np);
 		return -EINVAL;
@@ -167,7 +173,7 @@ static int scmi_clocks_probe(struct scmi_device *sdev)
 		if (!sclk)
 			return -ENOMEM;
 
-		sclk->info = handle->clk_ops->info_get(handle, idx);
+		sclk->info = clk_ops->info_get(handle, idx);
 		if (!sclk->info) {
 			dev_dbg(dev, "invalid clock info for idx %d\n", idx);
 			continue;
@@ -191,6 +197,13 @@ static int scmi_clocks_probe(struct scmi_device *sdev)
 					   clk_data);
 }
 
+static void scmi_clocks_remove(struct scmi_device *sdev)
+{
+	const struct scmi_handle *handle = sdev->handle;
+
+	handle->put_ops(handle, SCMI_PROTOCOL_CLOCK);
+}
+
 static const struct scmi_device_id scmi_id_table[] = {
 	{ SCMI_PROTOCOL_CLOCK, "clocks" },
 	{ },
@@ -200,6 +213,7 @@ MODULE_DEVICE_TABLE(scmi, scmi_id_table);
 static struct scmi_driver scmi_clocks_driver = {
 	.name = "scmi-clocks",
 	.probe = scmi_clocks_probe,
+	.remove = scmi_clocks_remove,
 	.id_table = scmi_id_table,
 };
 module_scmi_driver(scmi_clocks_driver);
diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c
index 46b268095421..280597b3c6fd 100644
--- a/drivers/cpufreq/scmi-cpufreq.c
+++ b/drivers/cpufreq/scmi-cpufreq.c
@@ -25,11 +25,11 @@ struct scmi_data {
 };
 
 static const struct scmi_handle *handle;
+static const struct scmi_perf_ops *perf_ops;
 
 static unsigned int scmi_cpufreq_get_rate(unsigned int cpu)
 {
 	struct cpufreq_policy *policy = cpufreq_cpu_get_raw(cpu);
-	const struct scmi_perf_ops *perf_ops = handle->perf_ops;
 	struct scmi_data *priv = policy->driver_data;
 	unsigned long rate;
 	int ret;
@@ -50,7 +50,6 @@ scmi_cpufreq_set_target(struct cpufreq_policy *policy, unsigned int index)
 {
 	int ret;
 	struct scmi_data *priv = policy->driver_data;
-	const struct scmi_perf_ops *perf_ops = handle->perf_ops;
 	u64 freq = policy->freq_table[index].frequency;
 
 	ret = perf_ops->freq_set(handle, priv->domain_id, freq * 1000, false);
@@ -64,7 +63,6 @@ static unsigned int scmi_cpufreq_fast_switch(struct cpufreq_policy *policy,
 					     unsigned int target_freq)
 {
 	struct scmi_data *priv = policy->driver_data;
-	const struct scmi_perf_ops *perf_ops = handle->perf_ops;
 
 	if (!perf_ops->freq_set(handle, priv->domain_id,
 				target_freq * 1000, true)) {
@@ -82,7 +80,7 @@ scmi_get_sharing_cpus(struct device *cpu_dev, struct cpumask *cpumask)
 	int cpu, domain, tdomain;
 	struct device *tcpu_dev;
 
-	domain = handle->perf_ops->device_domain_id(cpu_dev);
+	domain = perf_ops->device_domain_id(cpu_dev);
 	if (domain < 0)
 		return domain;
 
@@ -94,7 +92,7 @@ scmi_get_sharing_cpus(struct device *cpu_dev, struct cpumask *cpumask)
 		if (!tcpu_dev)
 			continue;
 
-		tdomain = handle->perf_ops->device_domain_id(tcpu_dev);
+		tdomain = perf_ops->device_domain_id(tcpu_dev);
 		if (tdomain == domain)
 			cpumask_set_cpu(cpu, cpumask);
 	}
@@ -109,13 +107,13 @@ scmi_get_cpu_power(unsigned long *power, unsigned long *KHz,
 	unsigned long Hz;
 	int ret, domain;
 
-	domain = handle->perf_ops->device_domain_id(cpu_dev);
+	domain = perf_ops->device_domain_id(cpu_dev);
 	if (domain < 0)
 		return domain;
 
 	/* Get the power cost of the performance domain. */
 	Hz = *KHz * 1000;
-	ret = handle->perf_ops->est_power_get(handle, domain, &Hz, power);
+	ret = perf_ops->est_power_get(handle, domain, &Hz, power);
 	if (ret)
 		return ret;
 
@@ -140,7 +138,7 @@ static int scmi_cpufreq_init(struct cpufreq_policy *policy)
 		return -ENODEV;
 	}
 
-	ret = handle->perf_ops->device_opps_add(handle, cpu_dev);
+	ret = perf_ops->device_opps_add(handle, cpu_dev);
 	if (ret) {
 		dev_warn(cpu_dev, "failed to add opps to the device\n");
 		return ret;
@@ -179,7 +177,7 @@ static int scmi_cpufreq_init(struct cpufreq_policy *policy)
 	}
 
 	priv->cpu_dev = cpu_dev;
-	priv->domain_id = handle->perf_ops->device_domain_id(cpu_dev);
+	priv->domain_id = perf_ops->device_domain_id(cpu_dev);
 
 	policy->driver_data = priv;
 	policy->freq_table = freq_table;
@@ -187,14 +185,14 @@ static int scmi_cpufreq_init(struct cpufreq_policy *policy)
 	/* SCMI allows DVFS request for any domain from any CPU */
 	policy->dvfs_possible_from_any_cpu = true;
 
-	latency = handle->perf_ops->transition_latency_get(handle, cpu_dev);
+	latency = perf_ops->transition_latency_get(handle, cpu_dev);
 	if (!latency)
 		latency = CPUFREQ_ETERNAL;
 
 	policy->cpuinfo.transition_latency = latency;
 
 	policy->fast_switch_possible =
-		handle->perf_ops->fast_switch_possible(handle, cpu_dev);
+		perf_ops->fast_switch_possible(handle, cpu_dev);
 
 	em_dev_register_perf_domain(cpu_dev, nr_opp, &em_cb, policy->cpus);
 
@@ -239,9 +237,13 @@ static int scmi_cpufreq_probe(struct scmi_device *sdev)
 
 	handle = sdev->handle;
 
-	if (!handle || !handle->perf_ops)
+	if (!handle)
 		return -ENODEV;
 
+	perf_ops = handle->get_ops(handle, SCMI_PROTOCOL_PERF);
+	if (IS_ERR(perf_ops))
+		return PTR_ERR(perf_ops);
+
 	ret = cpufreq_register_driver(&scmi_cpufreq_driver);
 	if (ret) {
 		dev_err(&sdev->dev, "%s: registering cpufreq failed, err: %d\n",
@@ -254,6 +256,8 @@ static int scmi_cpufreq_probe(struct scmi_device *sdev)
 static void scmi_cpufreq_remove(struct scmi_device *sdev)
 {
 	cpufreq_unregister_driver(&scmi_cpufreq_driver);
+
+	handle->put_ops(handle, SCMI_PROTOCOL_PERF);
 }
 
 static const struct scmi_device_id scmi_id_table[] = {
diff --git a/drivers/firmware/arm_scmi/base.c b/drivers/firmware/arm_scmi/base.c
index f19e08ed4369..129633e6fff4 100644
--- a/drivers/firmware/arm_scmi/base.c
+++ b/drivers/firmware/arm_scmi/base.c
@@ -318,7 +318,7 @@ static const struct scmi_event_ops base_event_ops = {
 	.fill_custom_report = scmi_base_fill_custom_report,
 };
 
-static int scmi_base_protocol_init(struct scmi_handle *h)
+static int scmi_base_protocol_init(const struct scmi_handle *h)
 {
 	int id, ret;
 	u8 *prot_imp;
diff --git a/drivers/firmware/arm_scmi/bus.c b/drivers/firmware/arm_scmi/bus.c
index afa2e4818a2b..3a2be1193c85 100644
--- a/drivers/firmware/arm_scmi/bus.c
+++ b/drivers/firmware/arm_scmi/bus.c
@@ -66,27 +66,11 @@ const struct scmi_protocol *scmi_get_protocol(int protocol_id)
 	return proto;
 }
 
-static int scmi_protocol_init(int protocol_id, struct scmi_handle *handle)
-{
-	const struct scmi_protocol *proto;
-
-	proto = idr_find(&scmi_available_protocols, protocol_id);
-	if (!proto)
-		return -EINVAL;
-	return proto->init(handle);
-}
-
-static int scmi_protocol_dummy_init(struct scmi_handle *handle)
-{
-	return 0;
-}
-
 static int scmi_dev_probe(struct device *dev)
 {
 	struct scmi_driver *scmi_drv = to_scmi_driver(dev->driver);
 	struct scmi_device *scmi_dev = to_scmi_dev(dev);
 	const struct scmi_device_id *id;
-	int ret;
 
 	id = scmi_dev_match_id(scmi_dev, scmi_drv);
 	if (!id)
@@ -95,14 +79,6 @@ static int scmi_dev_probe(struct device *dev)
 	if (!scmi_dev->handle)
 		return -EPROBE_DEFER;
 
-	ret = scmi_protocol_init(scmi_dev->protocol_id, scmi_dev->handle);
-	if (ret)
-		return ret;
-
-	/* Skip protocol initialisation for additional devices */
-	idr_replace(&scmi_available_protocols, &scmi_protocol_dummy_init,
-		    scmi_dev->protocol_id);
-
 	return scmi_drv->probe(scmi_dev);
 }
 
diff --git a/drivers/firmware/arm_scmi/clock.c b/drivers/firmware/arm_scmi/clock.c
index 4e8dafc36d7e..539c94860b8f 100644
--- a/drivers/firmware/arm_scmi/clock.c
+++ b/drivers/firmware/arm_scmi/clock.c
@@ -332,7 +332,7 @@ static const struct scmi_clk_ops clk_ops = {
 	.disable = scmi_clock_disable,
 };
 
-static int scmi_clock_protocol_init(struct scmi_handle *handle)
+static int scmi_clock_protocol_init(const struct scmi_handle *handle)
 {
 	u32 version;
 	int clkid, ret;
@@ -363,8 +363,6 @@ static int scmi_clock_protocol_init(struct scmi_handle *handle)
 	}
 
 	cinfo->version = version;
-	handle->clk_ops = &clk_ops;
-
 	return scmi_set_proto_priv(handle, SCMI_PROTOCOL_CLOCK, cinfo);
 }
 
diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
index de2f22032a57..56ebb710ee84 100644
--- a/drivers/firmware/arm_scmi/common.h
+++ b/drivers/firmware/arm_scmi/common.h
@@ -158,7 +158,7 @@ int scmi_version_get(const struct scmi_handle *h, u8 protocol, u32 *version);
 void scmi_setup_protocol_implemented(const struct scmi_handle *handle,
 				     u8 *prot_imp);
 
-typedef int (*scmi_prot_init_fn_t)(struct scmi_handle *);
+typedef int (*scmi_prot_init_fn_t)(const struct scmi_handle *);
 
 /**
  * struct scmi_protocol  - Protocol descriptor
@@ -202,8 +202,8 @@ void __exit scmi_##name##_unregister(void) \
 
 const struct scmi_protocol *scmi_get_protocol(int protocol_id);
 
-int scmi_acquire_protocol(struct scmi_handle *handle, u8 protocol_id);
-void scmi_release_protocol(struct scmi_handle *handle, u8 protocol_id);
+int scmi_acquire_protocol(const struct scmi_handle *handle, u8 protocol_id);
+void scmi_release_protocol(const struct scmi_handle *handle, u8 protocol_id);
 
 void *scmi_get_proto_priv(const struct scmi_handle *h, u8 prot);
 int scmi_set_proto_priv(const struct scmi_handle *handle, const u8 proto,
diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index bad1d0130e96..049220efd227 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -585,7 +585,7 @@ void *scmi_get_proto_priv(const struct scmi_handle *handle, u8 protocol_id)
  * Return: A reference to an initialized protocol instance or error on failure.
  */
 static struct scmi_protocol_instance * __must_check
-scmi_get_protocol_instance(struct scmi_handle *handle, u8 protocol_id)
+scmi_get_protocol_instance(const struct scmi_handle *handle, u8 protocol_id)
 {
 	int ret = -ENOMEM;
 	void *gid;
@@ -655,7 +655,7 @@ scmi_get_protocol_instance(struct scmi_handle *handle, u8 protocol_id)
  *
  * Return: 0 if protocol was acquired successfully.
  */
-int scmi_acquire_protocol(struct scmi_handle *handle, u8 protocol_id)
+int scmi_acquire_protocol(const struct scmi_handle *handle, u8 protocol_id)
 {
 	return IS_ERR(scmi_get_protocol_instance(handle, protocol_id));
 }
@@ -668,7 +668,7 @@ int scmi_acquire_protocol(struct scmi_handle *handle, u8 protocol_id)
  * Remove one user for the specified protocol and triggers de-initialization
  * and resources de-allocation once the last user has gone.
  */
-void scmi_release_protocol(struct scmi_handle *handle, u8 protocol_id)
+void scmi_release_protocol(const struct scmi_handle *handle, u8 protocol_id)
 {
 	struct scmi_info *info = handle_to_scmi_info(handle);
 	struct scmi_protocol_instance *pi;
@@ -700,6 +700,29 @@ void scmi_release_protocol(struct scmi_handle *handle, u8 protocol_id)
 	mutex_unlock(&info->protocols_mtx);
 }
 
+/**
+ * scmi_get_protocol_operations  - Get protocol operations
+ * @handle: A reference to the SCMI platform instance.
+ * @protocol_id: The protocol being requested.
+ *
+ * Get hold of a protocol accounting for its usage, eventually triggering its
+ * initialization, and returning the protocol specific operations.
+ *
+ * Return: A reference to the requested protocol operations or error.
+ *	   Must be checked for errors by caller.
+ */
+static const void __must_check
+*scmi_get_protocol_operations(const struct scmi_handle *handle, u8 protocol_id)
+{
+	struct scmi_protocol_instance *pi;
+
+	pi = scmi_get_protocol_instance(handle, protocol_id);
+	if (IS_ERR(pi))
+		return pi;
+
+	return pi->proto->ops;
+}
+
 void scmi_setup_protocol_implemented(const struct scmi_handle *handle,
 				     u8 *prot_imp)
 {
@@ -975,6 +998,8 @@ static int scmi_probe(struct platform_device *pdev)
 	handle = &info->handle;
 	handle->dev = info->dev;
 	handle->version = &info->version;
+	handle->get_ops = scmi_get_protocol_operations;
+	handle->put_ops = scmi_release_protocol;
 
 	ret = scmi_txrx_setup(info, dev, SCMI_PROTOCOL_BASE);
 	if (ret)
diff --git a/drivers/firmware/arm_scmi/notify.c b/drivers/firmware/arm_scmi/notify.c
index eae58b2a92cc..02b00af9b08f 100644
--- a/drivers/firmware/arm_scmi/notify.c
+++ b/drivers/firmware/arm_scmi/notify.c
@@ -367,7 +367,7 @@ static struct scmi_event_handler *
 scmi_get_active_handler(struct scmi_notify_instance *ni, u32 evt_key);
 static void scmi_put_active_handler(struct scmi_notify_instance *ni,
 				    struct scmi_event_handler *hndl);
-static void scmi_put_handler_unlocked(struct scmi_notify_instance *ni,
+static bool scmi_put_handler_unlocked(struct scmi_notify_instance *ni,
 				      struct scmi_event_handler *hndl);
 
 /**
@@ -899,9 +899,21 @@ static inline int scmi_bind_event_handler(struct scmi_notify_instance *ni,
 	if (!r_evt)
 		return -EINVAL;
 
-	/* Remove from pending and insert into registered */
+	/*
+	 * Remove from pending and insert into registered while getting hold
+	 * of protocol instance.
+	 */
 	hash_del(&hndl->hash);
+	/*
+	 * Acquire protocols only for NON pending handlers, so as NOT to trigger
+	 * protocol initialization when a notifier is registered against a still
+	 * not registered protocol, since it would make little sense to force init
+	 * protocols for which still no SCMI driver user exists: they wouldn't
+	 * emit any event anyway till some SCMI driver starts using it.
+	 */
+	scmi_acquire_protocol(ni->handle, KEY_XTRACT_PROTO_ID(hndl->key));
 	hndl->r_evt = r_evt;
+
 	mutex_lock(&r_evt->proto->registered_mtx);
 	hash_add(r_evt->proto->registered_events_handlers,
 		 &hndl->hash, hndl->key);
@@ -1192,41 +1204,65 @@ static int scmi_disable_events(struct scmi_event_handler *hndl)
  * * unregister and free the handler itself
  *
  * Context: Assumes all the proper locking has been managed by the caller.
+ *
+ * Return: True if handler was freed (users dropped to zero)
  */
-static void scmi_put_handler_unlocked(struct scmi_notify_instance *ni,
+static bool scmi_put_handler_unlocked(struct scmi_notify_instance *ni,
 				      struct scmi_event_handler *hndl)
 {
+	bool freed = false;
+
 	if (refcount_dec_and_test(&hndl->users)) {
 		if (!IS_HNDL_PENDING(hndl))
 			scmi_disable_events(hndl);
 		scmi_free_event_handler(hndl);
+		freed = true;
 	}
+
+	return freed;
 }
 
 static void scmi_put_handler(struct scmi_notify_instance *ni,
 			     struct scmi_event_handler *hndl)
 {
+	bool freed;
+	u8 protocol_id;
 	struct scmi_registered_event *r_evt = hndl->r_evt;
 
 	mutex_lock(&ni->pending_mtx);
-	if (r_evt)
+	if (r_evt) {
+		protocol_id = r_evt->proto->id;
 		mutex_lock(&r_evt->proto->registered_mtx);
+	}
 
-	scmi_put_handler_unlocked(ni, hndl);
+	freed = scmi_put_handler_unlocked(ni, hndl);
 
-	if (r_evt)
+	if (r_evt) {
 		mutex_unlock(&r_evt->proto->registered_mtx);
+		/*
+		 * Only registered handler acquired protocol; must be here
+		 * released only AFTER unlocking registered_mtx, since
+		 * releasing a protocol can trigger its de-initialization
+		 * (ie. including r_evt and registered_mtx)
+		 */
+		if (freed)
+			scmi_release_protocol(ni->handle, protocol_id);
+	}
 	mutex_unlock(&ni->pending_mtx);
 }
 
 static void scmi_put_active_handler(struct scmi_notify_instance *ni,
 				    struct scmi_event_handler *hndl)
 {
+	bool freed;
 	struct scmi_registered_event *r_evt = hndl->r_evt;
+	u8 protocol_id = r_evt->proto->id;
 
 	mutex_lock(&r_evt->proto->registered_mtx);
-	scmi_put_handler_unlocked(ni, hndl);
+	freed = scmi_put_handler_unlocked(ni, hndl);
 	mutex_unlock(&r_evt->proto->registered_mtx);
+	if (freed)
+		scmi_release_protocol(ni->handle, protocol_id);
 }
 
 /**
diff --git a/drivers/firmware/arm_scmi/perf.c b/drivers/firmware/arm_scmi/perf.c
index 13e215f359fb..bd9cb2583557 100644
--- a/drivers/firmware/arm_scmi/perf.c
+++ b/drivers/firmware/arm_scmi/perf.c
@@ -857,7 +857,7 @@ static const struct scmi_event_ops perf_event_ops = {
 	.fill_custom_report = scmi_perf_fill_custom_report,
 };
 
-static int scmi_perf_protocol_init(struct scmi_handle *handle)
+static int scmi_perf_protocol_init(const struct scmi_handle *handle)
 {
 	int domain;
 	u32 version;
@@ -896,7 +896,6 @@ static int scmi_perf_protocol_init(struct scmi_handle *handle)
 				      pinfo->num_domains);
 
 	pinfo->version = version;
-	handle->perf_ops = &perf_ops;
 	return scmi_set_proto_priv(handle, SCMI_PROTOCOL_PERF, pinfo);
 }
 
diff --git a/drivers/firmware/arm_scmi/power.c b/drivers/firmware/arm_scmi/power.c
index e0b29ed4e09a..1e026b5530a7 100644
--- a/drivers/firmware/arm_scmi/power.c
+++ b/drivers/firmware/arm_scmi/power.c
@@ -262,7 +262,7 @@ static const struct scmi_event_ops power_event_ops = {
 	.fill_custom_report = scmi_power_fill_custom_report,
 };
 
-static int scmi_power_protocol_init(struct scmi_handle *handle)
+static int scmi_power_protocol_init(const struct scmi_handle *handle)
 {
 	int domain;
 	u32 version;
@@ -297,7 +297,6 @@ static int scmi_power_protocol_init(struct scmi_handle *handle)
 				      pinfo->num_domains);
 
 	pinfo->version = version;
-	handle->power_ops = &power_ops;
 	return scmi_set_proto_priv(handle, SCMI_PROTOCOL_POWER, pinfo);
 }
 
diff --git a/drivers/firmware/arm_scmi/reset.c b/drivers/firmware/arm_scmi/reset.c
index f70e9b5108d5..b7da4de0e56e 100644
--- a/drivers/firmware/arm_scmi/reset.c
+++ b/drivers/firmware/arm_scmi/reset.c
@@ -274,7 +274,7 @@ static const struct scmi_event_ops reset_event_ops = {
 	.fill_custom_report = scmi_reset_fill_custom_report,
 };
 
-static int scmi_reset_protocol_init(struct scmi_handle *handle)
+static int scmi_reset_protocol_init(const struct scmi_handle *handle)
 {
 	int domain;
 	u32 version;
@@ -309,7 +309,6 @@ static int scmi_reset_protocol_init(struct scmi_handle *handle)
 				      pinfo->num_domains);
 
 	pinfo->version = version;
-	handle->reset_ops = &reset_ops;
 	return scmi_set_proto_priv(handle, SCMI_PROTOCOL_RESET, pinfo);
 }
 
diff --git a/drivers/firmware/arm_scmi/scmi_pm_domain.c b/drivers/firmware/arm_scmi/scmi_pm_domain.c
index 9e44479f0284..bfea56f77890 100644
--- a/drivers/firmware/arm_scmi/scmi_pm_domain.c
+++ b/drivers/firmware/arm_scmi/scmi_pm_domain.c
@@ -2,7 +2,7 @@
 /*
  * SCMI Generic power domain support.
  *
- * Copyright (C) 2018 ARM Ltd.
+ * Copyright (C) 2018-2020 ARM Ltd.
  */
 
 #include <linux/err.h>
@@ -11,6 +11,8 @@
 #include <linux/pm_domain.h>
 #include <linux/scmi_protocol.h>
 
+static const struct scmi_power_ops *power_ops;
+
 struct scmi_pm_domain {
 	struct generic_pm_domain genpd;
 	const struct scmi_handle *handle;
@@ -25,16 +27,15 @@ static int scmi_pd_power(struct generic_pm_domain *domain, bool power_on)
 	int ret;
 	u32 state, ret_state;
 	struct scmi_pm_domain *pd = to_scmi_pd(domain);
-	const struct scmi_power_ops *ops = pd->handle->power_ops;
 
 	if (power_on)
 		state = SCMI_POWER_STATE_GENERIC_ON;
 	else
 		state = SCMI_POWER_STATE_GENERIC_OFF;
 
-	ret = ops->state_set(pd->handle, pd->domain, state);
+	ret = power_ops->state_set(pd->handle, pd->domain, state);
 	if (!ret)
-		ret = ops->state_get(pd->handle, pd->domain, &ret_state);
+		ret = power_ops->state_get(pd->handle, pd->domain, &ret_state);
 	if (!ret && state != ret_state)
 		return -EIO;
 
@@ -61,10 +62,14 @@ static int scmi_pm_domain_probe(struct scmi_device *sdev)
 	struct generic_pm_domain **domains;
 	const struct scmi_handle *handle = sdev->handle;
 
-	if (!handle || !handle->power_ops)
+	if (!handle)
 		return -ENODEV;
 
-	num_domains = handle->power_ops->num_domains_get(handle);
+	power_ops = handle->get_ops(handle, SCMI_PROTOCOL_POWER);
+	if (IS_ERR(power_ops))
+		return PTR_ERR(power_ops);
+
+	num_domains = power_ops->num_domains_get(handle);
 	if (num_domains < 0) {
 		dev_err(dev, "number of domains not found\n");
 		return num_domains;
@@ -85,14 +90,14 @@ static int scmi_pm_domain_probe(struct scmi_device *sdev)
 	for (i = 0; i < num_domains; i++, scmi_pd++) {
 		u32 state;
 
-		if (handle->power_ops->state_get(handle, i, &state)) {
+		if (power_ops->state_get(handle, i, &state)) {
 			dev_warn(dev, "failed to get state for domain %d\n", i);
 			continue;
 		}
 
 		scmi_pd->domain = i;
 		scmi_pd->handle = handle;
-		scmi_pd->name = handle->power_ops->name_get(handle, i);
+		scmi_pd->name = power_ops->name_get(handle, i);
 		scmi_pd->genpd.name = scmi_pd->name;
 		scmi_pd->genpd.power_off = scmi_pd_power_off;
 		scmi_pd->genpd.power_on = scmi_pd_power_on;
@@ -111,6 +116,13 @@ static int scmi_pm_domain_probe(struct scmi_device *sdev)
 	return 0;
 }
 
+static void scmi_pm_domain_remove(struct scmi_device *sdev)
+{
+	const struct scmi_handle *handle = sdev->handle;
+
+	handle->put_ops(handle, SCMI_PROTOCOL_POWER);
+}
+
 static const struct scmi_device_id scmi_id_table[] = {
 	{ SCMI_PROTOCOL_POWER, "genpd" },
 	{ },
@@ -120,6 +132,7 @@ MODULE_DEVICE_TABLE(scmi, scmi_id_table);
 static struct scmi_driver scmi_power_domain_driver = {
 	.name = "scmi-power-domain",
 	.probe = scmi_pm_domain_probe,
+	.remove = scmi_pm_domain_remove,
 	.id_table = scmi_id_table,
 };
 module_scmi_driver(scmi_power_domain_driver);
diff --git a/drivers/firmware/arm_scmi/sensors.c b/drivers/firmware/arm_scmi/sensors.c
index 8a0a599558ba..e0129dcd322f 100644
--- a/drivers/firmware/arm_scmi/sensors.c
+++ b/drivers/firmware/arm_scmi/sensors.c
@@ -334,7 +334,7 @@ static const struct scmi_event_ops sensor_event_ops = {
 	.fill_custom_report = scmi_sensor_fill_custom_report,
 };
 
-static int scmi_sensors_protocol_init(struct scmi_handle *handle)
+static int scmi_sensors_protocol_init(const struct scmi_handle *handle)
 {
 	u32 version;
 	struct sensors_info *sinfo;
@@ -364,7 +364,6 @@ static int scmi_sensors_protocol_init(struct scmi_handle *handle)
 				      sinfo->num_sensors);
 
 	sinfo->version = version;
-	handle->sensor_ops = &sensor_ops;
 	return scmi_set_proto_priv(handle, SCMI_PROTOCOL_SENSOR, sinfo);
 }
 
diff --git a/drivers/firmware/arm_scmi/system.c b/drivers/firmware/arm_scmi/system.c
index 8f53f93c63ca..30e3510c1f07 100644
--- a/drivers/firmware/arm_scmi/system.c
+++ b/drivers/firmware/arm_scmi/system.c
@@ -101,7 +101,7 @@ static const struct scmi_event_ops system_event_ops = {
 	.fill_custom_report = scmi_system_fill_custom_report,
 };
 
-static int scmi_system_protocol_init(struct scmi_handle *handle)
+static int scmi_system_protocol_init(const struct scmi_handle *handle)
 {
 	u32 version;
 	struct scmi_system_info *pinfo;
diff --git a/drivers/hwmon/scmi-hwmon.c b/drivers/hwmon/scmi-hwmon.c
index d421e691318b..27ef71996a15 100644
--- a/drivers/hwmon/scmi-hwmon.c
+++ b/drivers/hwmon/scmi-hwmon.c
@@ -2,7 +2,7 @@
 /*
  * System Control and Management Interface(SCMI) based hwmon sensor driver
  *
- * Copyright (C) 2018 ARM Ltd.
+ * Copyright (C) 2018-2020 ARM Ltd.
  * Sudeep Holla <sudeep.holla@arm.com>
  */
 
@@ -13,6 +13,8 @@
 #include <linux/sysfs.h>
 #include <linux/thermal.h>
 
+static const struct scmi_sensor_ops *sensor_ops;
+
 struct scmi_sensors {
 	const struct scmi_handle *handle;
 	const struct scmi_sensor_info **info[hwmon_max];
@@ -72,7 +74,7 @@ static int scmi_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
 	const struct scmi_handle *h = scmi_sensors->handle;
 
 	sensor = *(scmi_sensors->info[type] + channel);
-	ret = h->sensor_ops->reading_get(h, sensor->id, &value);
+	ret = sensor_ops->reading_get(h, sensor->id, &value);
 	if (ret)
 		return ret;
 
@@ -170,10 +172,14 @@ static int scmi_hwmon_probe(struct scmi_device *sdev)
 	const struct hwmon_channel_info **ptr_scmi_ci;
 	const struct scmi_handle *handle = sdev->handle;
 
-	if (!handle || !handle->sensor_ops)
+	if (!handle)
 		return -ENODEV;
 
-	nr_sensors = handle->sensor_ops->count_get(handle);
+	sensor_ops = handle->get_ops(handle, SCMI_PROTOCOL_SENSOR);
+	if (IS_ERR(sensor_ops))
+		return PTR_ERR(sensor_ops);
+
+	nr_sensors = sensor_ops->count_get(handle);
 	if (!nr_sensors)
 		return -EIO;
 
@@ -184,7 +190,7 @@ static int scmi_hwmon_probe(struct scmi_device *sdev)
 	scmi_sensors->handle = handle;
 
 	for (i = 0; i < nr_sensors; i++) {
-		sensor = handle->sensor_ops->info_get(handle, i);
+		sensor = sensor_ops->info_get(handle, i);
 		if (!sensor)
 			return -EINVAL;
 
@@ -234,7 +240,7 @@ static int scmi_hwmon_probe(struct scmi_device *sdev)
 	}
 
 	for (i = nr_sensors - 1; i >= 0 ; i--) {
-		sensor = handle->sensor_ops->info_get(handle, i);
+		sensor = sensor_ops->info_get(handle, i);
 		if (!sensor)
 			continue;
 
@@ -258,6 +264,13 @@ static int scmi_hwmon_probe(struct scmi_device *sdev)
 	return PTR_ERR_OR_ZERO(hwdev);
 }
 
+static void scmi_hwmon_remove(struct scmi_device *sdev)
+{
+	const struct scmi_handle *handle = sdev->handle;
+
+	handle->put_ops(handle, SCMI_PROTOCOL_SENSOR);
+}
+
 static const struct scmi_device_id scmi_id_table[] = {
 	{ SCMI_PROTOCOL_SENSOR, "hwmon" },
 	{ },
@@ -267,6 +280,7 @@ MODULE_DEVICE_TABLE(scmi, scmi_id_table);
 static struct scmi_driver scmi_hwmon_drv = {
 	.name		= "scmi-hwmon",
 	.probe		= scmi_hwmon_probe,
+	.remove		= scmi_hwmon_remove,
 	.id_table	= scmi_id_table,
 };
 module_scmi_driver(scmi_hwmon_drv);
diff --git a/drivers/reset/reset-scmi.c b/drivers/reset/reset-scmi.c
index 8d3a858e3b19..e48220dedb35 100644
--- a/drivers/reset/reset-scmi.c
+++ b/drivers/reset/reset-scmi.c
@@ -2,7 +2,7 @@
 /*
  * ARM System Control and Management Interface (ARM SCMI) reset driver
  *
- * Copyright (C) 2019 ARM Ltd.
+ * Copyright (C) 2019-2020 ARM Ltd.
  */
 
 #include <linux/module.h>
@@ -11,6 +11,8 @@
 #include <linux/reset-controller.h>
 #include <linux/scmi_protocol.h>
 
+static const struct scmi_reset_ops *reset_ops;
+
 /**
  * struct scmi_reset_data - reset controller information structure
  * @rcdev: reset controller entity
@@ -39,7 +41,7 @@ scmi_reset_assert(struct reset_controller_dev *rcdev, unsigned long id)
 {
 	const struct scmi_handle *handle = to_scmi_handle(rcdev);
 
-	return handle->reset_ops->assert(handle, id);
+	return reset_ops->assert(handle, id);
 }
 
 /**
@@ -57,7 +59,7 @@ scmi_reset_deassert(struct reset_controller_dev *rcdev, unsigned long id)
 {
 	const struct scmi_handle *handle = to_scmi_handle(rcdev);
 
-	return handle->reset_ops->deassert(handle, id);
+	return reset_ops->deassert(handle, id);
 }
 
 /**
@@ -75,7 +77,7 @@ scmi_reset_reset(struct reset_controller_dev *rcdev, unsigned long id)
 {
 	const struct scmi_handle *handle = to_scmi_handle(rcdev);
 
-	return handle->reset_ops->reset(handle, id);
+	return reset_ops->reset(handle, id);
 }
 
 static const struct reset_control_ops scmi_reset_ops = {
@@ -91,9 +93,13 @@ static int scmi_reset_probe(struct scmi_device *sdev)
 	struct device_node *np = dev->of_node;
 	const struct scmi_handle *handle = sdev->handle;
 
-	if (!handle || !handle->reset_ops)
+	if (!handle)
 		return -ENODEV;
 
+	reset_ops = handle->get_ops(handle, SCMI_PROTOCOL_RESET);
+	if (IS_ERR(reset_ops))
+		return PTR_ERR(reset_ops);
+
 	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
 	if (!data)
 		return -ENOMEM;
@@ -101,12 +107,19 @@ static int scmi_reset_probe(struct scmi_device *sdev)
 	data->rcdev.ops = &scmi_reset_ops;
 	data->rcdev.owner = THIS_MODULE;
 	data->rcdev.of_node = np;
-	data->rcdev.nr_resets = handle->reset_ops->num_domains_get(handle);
+	data->rcdev.nr_resets = reset_ops->num_domains_get(handle);
 	data->handle = handle;
 
 	return devm_reset_controller_register(dev, &data->rcdev);
 }
 
+static void scmi_reset_remove(struct scmi_device *sdev)
+{
+	const struct scmi_handle *handle = sdev->handle;
+
+	handle->put_ops(handle, SCMI_PROTOCOL_RESET);
+}
+
 static const struct scmi_device_id scmi_id_table[] = {
 	{ SCMI_PROTOCOL_RESET, "reset" },
 	{ },
@@ -116,6 +129,7 @@ MODULE_DEVICE_TABLE(scmi, scmi_id_table);
 static struct scmi_driver scmi_reset_driver = {
 	.name = "scmi-reset",
 	.probe = scmi_reset_probe,
+	.remove = scmi_reset_remove,
 	.id_table = scmi_id_table,
 };
 module_scmi_driver(scmi_reset_driver);
diff --git a/include/linux/scmi_protocol.h b/include/linux/scmi_protocol.h
index bc4f06d46bfb..bfe7017cff19 100644
--- a/include/linux/scmi_protocol.h
+++ b/include/linux/scmi_protocol.h
@@ -257,11 +257,6 @@ struct scmi_notify_ops {
  *
  * @dev: pointer to the SCMI device
  * @version: pointer to the structure containing SCMI version information
- * @power_ops: pointer to set of power protocol operations
- * @perf_ops: pointer to set of performance protocol operations
- * @clk_ops: pointer to set of clock protocol operations
- * @sensor_ops: pointer to set of sensor protocol operations
- * @reset_ops: pointer to set of reset protocol operations
  * @notify_ops: pointer to set of notifications related operations
  * @notify_priv: pointer to private data structure specific to notifications
  *	(for internal use only)
@@ -269,11 +264,11 @@ struct scmi_notify_ops {
 struct scmi_handle {
 	struct device *dev;
 	struct scmi_revision_info *version;
-	const struct scmi_perf_ops *perf_ops;
-	const struct scmi_clk_ops *clk_ops;
-	const struct scmi_power_ops *power_ops;
-	const struct scmi_sensor_ops *sensor_ops;
-	const struct scmi_reset_ops *reset_ops;
+
+	const void __must_check *(*get_ops)(const struct scmi_handle *handle,
+					    u8 proto);
+	void (*put_ops)(const struct scmi_handle *handle, u8 proto);
+
 	const struct scmi_notify_ops *notify_ops;
 	void *notify_priv;
 };
-- 
2.17.1