[PATCH v10 4/7] i3c: master: add mastership handover support

Parshuram Thombare
2020-11-30T06:20:09Z

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