[PATCH v9 4/7] i3c: master: add mastership handover support

[Parshuram Thombare <pthombar@cadence.com>]

Added mastership acquire and yield functions.

Signed-off-by: Parshuram Thombare <pthombar@cadence.com>
---
 drivers/i3c/master.c       |  183 +++++++++++++++++++++++++++++++++++++++++---
 include/linux/i3c/master.h |    6 ++
 2 files changed, 177 insertions(+), 12 deletions(-)

diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
index af0630a..51ef706 100644
--- a/drivers/i3c/master.c
+++ b/drivers/i3c/master.c
@@ -44,6 +44,16 @@ static void i3c_bus_maintenance_lock(struct i3c_bus *bus)
 }
 
 /**
+ * i3c_bus_maintenance_downgrade_lock - Downgrade maintenance lock to
+ * normaluse lock.
+ * @bus: I3C bus to take the lock on
+ */
+static void i3c_bus_maintenance_downgrade_lock(struct i3c_bus *bus)
+{
+	downgrade_write(&bus->lock);
+}
+
+/**
  * i3c_bus_maintenance_unlock - Release the bus lock after a maintenance
  *			      operation
  * @bus: I3C bus to release the lock on
@@ -451,6 +461,59 @@ static int i3c_bus_init(struct i3c_bus *i3cbus)
 	[I3C_BUS_MODE_MIXED_SLOW] = "mixed-slow",
 };
 
+static int i3c_master_enable_mr_events(struct i3c_master_controller *master)
+{
+	int ret;
+
+	master->ops->enable_mr_events(master);
+	i3c_bus_maintenance_lock(&master->bus);
+	ret = i3c_master_enec_locked(master, I3C_BROADCAST_ADDR,
+				     I3C_CCC_EVENT_MR | I3C_CCC_EVENT_HJ);
+	i3c_bus_maintenance_unlock(&master->bus);
+
+	return ret;
+}
+
+/**
+ * i3c_master_acquire_bus() - acquire I3C bus mastership
+ * @m: I3C master object
+ *
+ * This function may sleep.
+ * It is expected to be called with normaluse_lock.
+ */
+static int i3c_master_acquire_bus(struct i3c_master_controller *m)
+{
+	int ret = 0;
+
+	/*
+	 * Request mastership needs maintenance(write) lock. So, to avoid
+	 * deadlock, release normaluse(read) lock, which is expected to be
+	 * held before calling this function.
+	 * normaluse(read) lock is expected to be held before calling
+	 * this function to avoid race with maintenance activities
+	 * like DEFSLVS processing etc
+	 */
+	i3c_bus_normaluse_unlock(&m->bus);
+	i3c_bus_maintenance_lock(&m->bus);
+
+	if (m->this && m->this == m->bus.cur_master) {
+		i3c_master_disec_locked(m, I3C_BROADCAST_ADDR,
+					I3C_CCC_EVENT_MR |
+					I3C_CCC_EVENT_HJ);
+		goto mr_req_done;
+	}
+
+	ret = m->ops->request_mastership(m);
+	if (ret)
+		goto mr_req_done;
+
+	m->bus.cur_master = m->this;
+
+mr_req_done:
+	i3c_bus_maintenance_downgrade_lock(&m->bus);
+	return ret;
+}
+
 static ssize_t mode_show(struct device *dev,
 			 struct device_attribute *da,
 			 char *buf)
@@ -476,11 +539,12 @@ static ssize_t current_master_show(struct device *dev,
 				   char *buf)
 {
 	struct i3c_bus *i3cbus = dev_to_i3cbus(dev);
-	ssize_t ret;
+	ssize_t ret = 0;
 
 	i3c_bus_normaluse_lock(i3cbus);
-	ret = sprintf(buf, "%d-%llx\n", i3cbus->id,
-		      i3cbus->cur_master->info.pid);
+	if (i3cbus->cur_master)
+		ret = sprintf(buf, "%d-%llx\n", i3cbus->id,
+			      i3cbus->cur_master->info.pid);
 	i3c_bus_normaluse_unlock(i3cbus);
 
 	return ret;
@@ -690,6 +754,33 @@ static int i3c_master_send_ccc_cmd_locked(struct i3c_master_controller *master,
 	return 0;
 }
 
+static int i3c_master_get_accmst_locked(struct i3c_master_controller *master,
+					u8 addr)
+{
+	struct i3c_ccc_getaccmst *accmst;
+	struct i3c_ccc_cmd_dest dest;
+	struct i3c_ccc_cmd cmd;
+	int ret;
+
+	accmst = i3c_ccc_cmd_dest_init(&dest, addr, sizeof(*accmst));
+	if (!accmst)
+		return -ENOMEM;
+
+	i3c_ccc_cmd_init(&cmd, true, I3C_CCC_GETACCMST, &dest, 1);
+
+	ret = i3c_master_send_ccc_cmd_locked(master, &cmd);
+	if (ret)
+		goto out;
+
+	if (dest.payload.len != sizeof(*accmst))
+		ret = -EIO;
+
+out:
+	i3c_ccc_cmd_dest_cleanup(&dest);
+
+	return ret;
+}
+
 static struct i2c_dev_desc *
 i3c_master_find_i2c_dev_by_addr(const struct i3c_master_controller *master,
 				u16 addr)
@@ -1582,10 +1673,6 @@ int i3c_master_set_info(struct i3c_master_controller *master,
 	if (!i3c_bus_dev_addr_is_avail(&master->bus, info->dyn_addr))
 		return -EINVAL;
 
-	if (I3C_BCR_DEVICE_ROLE(info->bcr) == I3C_BCR_I3C_MASTER &&
-	    master->secondary)
-		return -EINVAL;
-
 	if (master->this)
 		return -EINVAL;
 
@@ -1594,7 +1681,9 @@ int i3c_master_set_info(struct i3c_master_controller *master,
 		return PTR_ERR(i3cdev);
 
 	master->this = i3cdev;
-	master->bus.cur_master = master->this;
+
+	if (!master->secondary)
+		master->bus.cur_master = master->this;
 
 	ret = i3c_master_attach_i3c_dev(master, i3cdev);
 	if (ret)
@@ -1637,6 +1726,74 @@ static void i3c_master_detach_free_devs(struct i3c_master_controller *master)
 }
 
 /**
+ * i3c_master_yield_bus() - yield I3C bus mastership
+ * @m: I3C master object
+ * @sec_mst_dyn_addr: address of device requesting mastership
+ *
+ * This function may sleep.
+ * It is expected to be called with normaluse_lock.
+ */
+void
+i3c_master_yield_bus(struct i3c_master_controller *m, u8 sec_mst_dyn_addr)
+{
+	struct i3c_dev_desc *i3cdev;
+	bool dev_found =  false;
+	int ret = 0;
+
+	i3c_bus_maintenance_lock(&m->bus);
+	if (m->this != m->bus.cur_master)
+		goto mr_yield_done;
+
+	i3c_bus_for_each_i3cdev(&m->bus, i3cdev) {
+		if (sec_mst_dyn_addr == i3cdev->info.dyn_addr) {
+			dev_found = true;
+			break;
+		}
+	}
+
+	/* Requesting device not found on i3c list. This should never happen. */
+	if (!dev_found)
+		goto mr_yield_done;
+
+	/*
+	 * Maintenance lock and master check above is used to
+	 * avoid race amongst devices sending MR requests
+	 * at the same time, as soon as ENEC MST is sent by the current
+	 * master. It ensure that only one MR request is processed,
+	 * rest MR requests on losing devices will timeout in wait MR
+	 * DONE state. And next MR requests are blocked due to DISEC MST
+	 * sent by current master in yield operation.
+	 * New master should send ENEC MST once it's work is done.
+	 * maintainanace lock is also needed for i3c_master_get_accmst_locked.
+	 */
+
+	ret = i3c_master_disec_locked(m, I3C_BROADCAST_ADDR,
+				      I3C_CCC_EVENT_MR |
+				      I3C_CCC_EVENT_HJ);
+	/*
+	 * Once mastership is given to the new master, it is expected that
+	 * MR is disabled prior to that and new master is responsible to
+	 * enable it by broadcasting ENEC MR when it's work is done.
+	 * If DISEC MR fails and we still go ahead with handover, chances
+	 * are new master will get interrupted by unexpected MR requests.
+	 */
+	if (ret)
+		goto mr_yield_done;
+
+	ret = i3c_master_get_accmst_locked(m, sec_mst_dyn_addr);
+	if (ret)
+		goto mr_yield_done;
+
+	m->bus.cur_master = i3cdev;
+
+mr_yield_done:
+	i3c_bus_maintenance_unlock(&m->bus);
+	if (ret)
+		i3c_master_enable_mr_events(m);
+}
+EXPORT_SYMBOL_GPL(i3c_master_yield_bus);
+
+/**
  * i3c_primary_master_bus_init() - initialize an I3C bus
  * @master: main master initializing the bus
  *
@@ -2522,6 +2679,9 @@ static int i3c_master_check_ops(const struct i3c_master_controller_ops *ops)
 	     !ops->recycle_ibi_slot))
 		return -EINVAL;
 
+	if (ops->request_mastership && !ops->enable_mr_events)
+		return -EINVAL;
+
 	return 0;
 }
 
@@ -2536,10 +2696,6 @@ static int i3c_master_init(struct i3c_master_controller *master,
 	struct i2c_dev_boardinfo *i2cbi;
 	int ret;
 
-	/* We do not support secondary masters yet. */
-	if (secondary)
-		return -ENOTSUPP;
-
 	ret = i3c_master_check_ops(ops);
 	if (ret)
 		return ret;
@@ -2665,6 +2821,9 @@ int i3c_primary_master_register(struct i3c_master_controller *master,
 	i3c_master_register_new_i3c_devs(master);
 	i3c_bus_normaluse_unlock(&master->bus);
 
+	if (ops->request_mastership)
+		ret = i3c_master_enable_mr_events(master);
+
 	return 0;
 
 err_del_dev:
diff --git a/include/linux/i3c/master.h b/include/linux/i3c/master.h
index e186d53..77c0422 100644
--- a/include/linux/i3c/master.h
+++ b/include/linux/i3c/master.h
@@ -426,6 +426,8 @@ struct i3c_bus {
  *		      for a future IBI
  *		      This method is mandatory only if ->request_ibi is not
  *		      NULL.
+ * @request_mastership: send mastership request to the current master
+ * @enable_mr_events: enable mastership request handling by the controller
  */
 struct i3c_master_controller_ops {
 	int (*bus_init)(struct i3c_master_controller *master);
@@ -452,6 +454,8 @@ struct i3c_master_controller_ops {
 	int (*disable_ibi)(struct i3c_dev_desc *dev);
 	void (*recycle_ibi_slot)(struct i3c_dev_desc *dev,
 				 struct i3c_ibi_slot *slot);
+	int (*request_mastership)(struct i3c_master_controller *master);
+	void (*enable_mr_events)(struct i3c_master_controller *m);
 };
 
 /**
@@ -517,6 +521,8 @@ struct i3c_master_controller {
 #define i3c_bus_for_each_i3cdev(bus, dev)				\
 	list_for_each_entry(dev, &(bus)->devs.i3c, common.node)
 
+void i3c_master_yield_bus(struct i3c_master_controller *m,
+			  u8 sec_mst_dyn_addr);
 int i3c_master_do_i2c_xfers(struct i3c_master_controller *master,
 			    const struct i2c_msg *xfers,
 			    int nxfers);
-- 
1.7.1