[PATCH v7 1/4] i2c-smbus : Add client discovered ARA support

[Marc CAPDEVILLE]

This is from rfc by Alan Cox : https://patchwork.ozlabs.org/patch/381773

The idea is as follows (extract from above rfc) :
- If an adapter knows about its ARA and smbus alerts then the adapter
  creates its own interrupt handler as before

- If a client knows it needs smbus alerts it calls
  i2c_require_smbus_alert(). This ensures that there is an ARA handler
  registered and tells the client whether the adapter is handling it
  anyway or not.

- When the client learns that an ARA event has occurred it calls
  i2c_smbus_alert_event() which uses the existing ARA mechanism to kick
  things off.

In addition, if a client have an irq line to trigger smbus alert, client
driver register its irq with i2c_smbus_alert_add_irq() to the smbus alert
driver to use the generic alert interrupt handler. On detach, the client
must unregister its irq from the smbus alert driver with
i2c_smbus_alert_free_irq().

Signed-off-by: Marc CAPDEVILLE <m.capdeville@xxxxxxxxxx>
---
 drivers/i2c/i2c-core-smbus.c |  42 +++++++++++
 drivers/i2c/i2c-smbus.c      | 171 +++++++++++++++++++++++++++++++++++++++++--
 include/linux/i2c-smbus.h    |  22 ++++++
 include/linux/i2c.h          |   2 +
 4 files changed, 232 insertions(+), 5 deletions(-)

diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
index 1238c94fe5a1..0d84ac9669e9 100644
--- a/drivers/i2c/i2c-core-smbus.c
+++ b/drivers/i2c/i2c-core-smbus.c
@@ -659,6 +659,48 @@ struct i2c_client *i2c_setup_smbus_alert(struct i2c_adapter *adapter,
 }
 EXPORT_SYMBOL_GPL(i2c_setup_smbus_alert);
 
+/**
+ * i2c_require_smbus_alert - Client discovered SMBus alert
+ * @client: client requiring ARA support
+ *
+ * When a client needs an ARA it calls this method. If the bus adapter
+ * supports ARA and already knows how to do so then it will already have
+ * configured for ARA and this is a no-op. If not then we set up an ARA
+ * on the adapter.
+ *
+ * Return:
+ *	0 if ARA support already registered
+ *	1 if call register a new smbus_alert device
+ *	<0 on error
+ */
+int i2c_require_smbus_alert(struct i2c_client *client)
+{
+	struct i2c_adapter *adapter = client->adapter;
+	struct i2c_smbus_alert_setup setup;
+	struct i2c_client *ara;
+	int ret;
+
+	if (adapter->smbus_ara) {
+		/*
+		 * ARA is already known and handled by the adapter (ideal case)
+		 * or another client has specified ARA is needed
+		 */
+		ret = 0;
+	} else {
+		/* First client requesting alert and no adapter has
+		 * has setup one
+		 */
+		setup.irq = 0;
+		ara = i2c_setup_smbus_alert(adapter, &setup);
+		if (!ara)
+			return -ENODEV;
+		ret = 1;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(i2c_require_smbus_alert);
+
 #if IS_ENABLED(CONFIG_I2C_SMBUS) && IS_ENABLED(CONFIG_OF)
 int of_i2c_setup_smbus_alert(struct i2c_adapter *adapter)
 {
diff --git a/drivers/i2c/i2c-smbus.c b/drivers/i2c/i2c-smbus.c
index 5a1dd7f13bac..1699333ac950 100644
--- a/drivers/i2c/i2c-smbus.c
+++ b/drivers/i2c/i2c-smbus.c
@@ -25,9 +25,16 @@
 #include <linux/slab.h>
 #include <linux/workqueue.h>
 
+struct i2c_smbus_irq_usage {
+	struct list_head	list;
+	int			irq;
+	int			count;
+};
+
 struct i2c_smbus_alert {
 	struct work_struct	alert;
 	struct i2c_client	*ara;		/* Alert response address */
+	struct list_head	irq_usage;	/* irq usage list */
 };
 
 struct alert_data {
@@ -126,6 +133,124 @@ static void smbalert_work(struct work_struct *work)
 
 }
 
+/**
+ * i2c_smbus_alert_add_irq - Add a new irq handler to ARA client
+ * @client: The client which want to add an smbus alert irq handler
+ * @irq: The irq number to be added to the smbus alert device
+ * return: 0 if irq handler already exist, 1 if a new handler has been
+ *	   registered, <0 on error
+ *
+ * This is used by the smbalert_probe and by smbus client to check if an
+ * irq handler already exist for that irq and if not register a new one
+ * Clients must free their irq with i2c_smbus_alert_free_irq() on driver
+ * detach.
+ */
+int i2c_smbus_alert_add_irq(struct i2c_client *client, int irq)
+{
+	int res;
+	struct i2c_smbus_irq_usage *irq_usage;
+	struct i2c_client *ara;
+	struct i2c_smbus_alert *alert;
+
+	ara = client->adapter->smbus_ara;
+	if (!ara)
+		return -EINVAL;
+
+	alert = i2c_get_clientdata(client->adapter->smbus_ara);
+	if (!alert)
+		return -EINVAL;
+
+	if (!irq)
+		return 0;
+
+	/* Check if handler exist for that irq */
+	list_for_each_entry(irq_usage, &alert->irq_usage, list)
+		if (irq_usage->irq == irq)
+			break;
+
+	if (irq_usage->irq == irq) {
+		irq_usage->count++;
+	} else {
+		/* setup a new handler for that irq */
+		res = devm_request_threaded_irq(&ara->dev, irq,
+						NULL, smbus_alert,
+						IRQF_SHARED | IRQF_ONESHOT,
+						"smbus_alert", alert);
+		if (res)
+			return res;
+
+		/* Add adapter irq number to used irq list with a count of 1 */
+		irq_usage = devm_kmalloc(&ara->dev,
+					 sizeof(struct i2c_smbus_irq_usage),
+					 GFP_KERNEL);
+		INIT_LIST_HEAD(&irq_usage->list);
+		irq_usage->irq = irq;
+		irq_usage->count = 1;
+		list_add(&irq_usage->list, &alert->irq_usage);
+
+		return 0;
+	}
+
+	return 1;
+}
+EXPORT_SYMBOL_GPL(i2c_smbus_alert_add_irq);
+
+/**
+ * i2c_smbus_alert_free_irq - free irq added with i2c_smbus_alert_add_irq()
+ * @client: The client which want to free its smbus alert irq
+ * @irq: The irq number to be freed
+ * return: 0 if irq handler still exist for other client,
+ *	   1 if client is the last one using this handler and handler have been
+ *	     removed,
+ *	   <0 on error.
+ *
+ * This is used by smbus clients to free their irq usage from smbus alert
+ * device.
+ */
+int i2c_smbus_alert_free_irq(struct i2c_client *client, int irq)
+{
+	struct i2c_smbus_irq_usage *irq_usage;
+	struct i2c_client *ara;
+	struct i2c_smbus_alert *alert;
+
+	ara = client->adapter->smbus_ara;
+	if (!ara)
+		return -EINVAL;
+
+	alert = i2c_get_clientdata(client->adapter->smbus_ara);
+	if (!alert)
+		return -EINVAL;
+
+	if (!irq)
+		return 0;
+
+	/* Check if handler exist for that irq */
+	list_for_each_entry(irq_usage, &alert->irq_usage, list)
+		if (irq_usage->irq == irq)
+			break;
+
+	if (irq_usage->irq == irq) {
+		irq_usage->count--;
+		if (!irq_usage->count) {
+			/* usage count goes to 0
+			 * so remove irq_usage from list
+			 */
+			list_del(&irq_usage->list);
+			devm_kfree(&ara->dev, irq_usage);
+
+			/* remove irq handler */
+			devm_free_irq(&ara->dev, irq, alert);
+
+			return 1;
+		}
+
+		return 0;
+	}
+
+	return -EINVAL;
+}
+EXPORT_SYMBOL_GPL(i2c_smbus_alert_free_irq);
+
 /* Setup SMBALERT# infrastructure */
 static int smbalert_probe(struct i2c_client *ara,
 			  const struct i2c_device_id *id)
@@ -151,16 +276,18 @@ static int smbalert_probe(struct i2c_client *ara,
 	INIT_WORK(&alert->alert, smbalert_work);
 	alert->ara = ara;
 
+	INIT_LIST_HEAD(&alert->irq_usage);
+
+	i2c_set_clientdata(ara, alert);
+
+	ara->adapter->smbus_ara = ara;
+
 	if (irq > 0) {
-		res = devm_request_threaded_irq(&ara->dev, irq,
-						NULL, smbus_alert,
-						IRQF_SHARED | IRQF_ONESHOT,
-						"smbus_alert", alert);
+		res = i2c_smbus_alert_add_irq(ara, irq);
 		if (res)
 			return res;
 	}
 
-	i2c_set_clientdata(ara, alert);
 	dev_info(&adapter->dev, "supports SMBALERT#\n");
 
 	return 0;
@@ -172,6 +299,9 @@ static int smbalert_remove(struct i2c_client *ara)
 	struct i2c_smbus_alert *alert = i2c_get_clientdata(ara);
 
 	cancel_work_sync(&alert->alert);
+
+	ara->adapter->smbus_ara = NULL;
+
 	return 0;
 }
 
@@ -210,6 +340,37 @@ int i2c_handle_smbus_alert(struct i2c_client *ara)
 }
 EXPORT_SYMBOL_GPL(i2c_handle_smbus_alert);
 
+/**
+ * i2c_smbus_alert_event
+ * @client: the client who known of a probable ARA event
+ * Context: can't sleep
+ *
+ * Helper function to be called from an I2C device driver's interrupt
+ * handler. It will schedule the alert work, in turn calling the
+ * corresponding I2C device driver's alert function.
+ *
+ * It is assumed that client is an i2c client who previously call
+ * i2c_require_smbus_alert().
+ *
+ * return: <0 on error
+ */
+int i2c_smbus_alert_event(struct i2c_client *client)
+{
+	struct i2c_client *ara;
+	struct i2c_smbus_alert *alert;
+
+	ara = client->adapter->smbus_ara;
+	if (!ara)
+		return -EINVAL;
+
+	alert = i2c_get_clientdata(ara);
+	if (!alert)
+		return -EINVAL;
+
+	return schedule_work(&alert->alert);
+}
+EXPORT_SYMBOL_GPL(i2c_smbus_alert_event);
+
 module_i2c_driver(smbalert_driver);
 
 MODULE_AUTHOR("Jean Delvare <jdelvare@xxxxxxx>");
diff --git a/include/linux/i2c-smbus.h b/include/linux/i2c-smbus.h
index fb0e040b1abb..cf777f29cc79 100644
--- a/include/linux/i2c-smbus.h
+++ b/include/linux/i2c-smbus.h
@@ -47,6 +47,7 @@ struct i2c_smbus_alert_setup {
 
 struct i2c_client *i2c_setup_smbus_alert(struct i2c_adapter *adapter,
 					 struct i2c_smbus_alert_setup *setup);
+int i2c_require_smbus_alert(struct i2c_client *client);
 int i2c_handle_smbus_alert(struct i2c_client *ara);
 
 #if IS_ENABLED(CONFIG_I2C_SMBUS) && IS_ENABLED(CONFIG_OF)
@@ -58,4 +59,25 @@ static inline int of_i2c_setup_smbus_alert(struct i2c_adapter *adap)
 }
 #endif
 
+#if IS_ENABLED(CONFIG_I2C_SMBUS)
+int i2c_smbus_alert_add_irq(struct i2c_client *client, int irq);
+int i2c_smbus_alert_free_irq(struct i2c_client *client, int irq);
+int i2c_smbus_alert_event(struct i2c_client *client);
+#else
+static inline int i2c_smbus_alert_add_irq(struct i2c_client *client, int irq)
+{
+	return -EINVAL;
+}
+
+static inline int i2c_smbus_alert_free_irq(struct i2c_client *client, int irq)
+{
+	return -EINVAL;
+}
+
+static inline int i2c_smbus_alert_event(struct i2c_client *client)
+{
+	return -EINVAL;
+}
+#endif
+
 #endif /* _LINUX_I2C_SMBUS_H */
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 5d7f3c1853ae..7592dce12923 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -652,6 +652,8 @@ struct i2c_adapter {
 	const struct i2c_adapter_quirks *quirks;
 
 	struct irq_domain *host_notify_domain;
+
+	struct i2c_client *smbus_ara;	/* ARA client address if any or NULL */
 };
 #define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)
 
-- 
2.11.0