[PATCH V2 5/6] slimbus: Add support for 'clock-pause' feature

[Sagar Dharia]

Per slimbus specification, a reconfiguration sequence known as
'clock pause' needs to be broadcast over the bus while entering low-
power mode. Clock-pause is initiated by the controller driver.
To exit clock-pause, controller typically wakes up the framer device.
Since wakeup precedure is controller-specific, framework calls it via
controller's function pointer to invoke it.

Signed-off-by: Sagar Dharia <sdharia@xxxxxxxxxxxxxx>
---
 drivers/slimbus/slimbus.c | 109 ++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/slimbus.h   |  65 +++++++++++++++++++++++++++
 2 files changed, 174 insertions(+)

diff --git a/drivers/slimbus/slimbus.c b/drivers/slimbus/slimbus.c
index d74dfec..3cfa414 100644
--- a/drivers/slimbus/slimbus.c
+++ b/drivers/slimbus/slimbus.c
@@ -436,7 +436,9 @@ static int slim_register_controller(struct slim_controller *ctrl)
 		ctrl->min_cg = SLIM_MIN_CLK_GEAR;
 	if (!ctrl->max_cg)
 		ctrl->max_cg = SLIM_MAX_CLK_GEAR;
+	init_completion(&ctrl->sched.pause_comp);
 	mutex_init(&ctrl->m_ctrl);
+	mutex_init(&ctrl->sched.m_reconf);
 	ret = device_register(&ctrl->dev);
 	if (ret)
 		goto out_list;
@@ -1059,6 +1061,113 @@ int slim_request_clear_inf_element(struct slim_device *sb,
 }
 EXPORT_SYMBOL(slim_request_clear_inf_element);
 
+/**
+ * slim_ctrl_clk_pause: Called by slimbus controller to enter/exit 'clock pause'
+ * Slimbus specification needs this sequence to turn-off clocks for the bus.
+ * The sequence involves sending 3 broadcast messages (reconfiguration
+ * sequence) to inform all devices on the bus.
+ * To exit clock-pause, controller typically wakes up active framer device.
+ * @ctrl: controller requesting bus to be paused or woken up
+ * @wakeup: Wakeup this controller from clock pause.
+ * @restart: Restart time value per spec used for clock pause. This value
+ *	isn't used when controller is to be woken up.
+ * This API executes clock pause reconfiguration sequence if wakeup is false.
+ * If wakeup is true, controller's wakeup is called.
+ * For entering clock-pause, -EBUSY is returned if a message txn in pending.
+ */
+int slim_ctrl_clk_pause(struct slim_controller *ctrl, bool wakeup, u8 restart)
+{
+	int i, ret = 0;
+	unsigned long flags;
+	struct slim_sched *sched = &ctrl->sched;
+	struct slim_val_inf msg = {0, 0, NULL, NULL, NULL, NULL};
+
+	DEFINE_SLIM_BCAST_TXN(txn, SLIM_MSG_MC_BEGIN_RECONFIGURATION,
+				3, SLIM_LA_MANAGER, &msg);
+
+	if (wakeup == false && restart > SLIM_CLK_UNSPECIFIED)
+		return -EINVAL;
+	mutex_lock(&sched->m_reconf);
+	if (wakeup) {
+		if (sched->clk_state == SLIM_CLK_ACTIVE) {
+			mutex_unlock(&sched->m_reconf);
+			return 0;
+		}
+		/**
+		 * Fine-tune calculation based on clock gear,
+		 * message-bandwidth after bandwidth management
+		 */
+		ret = wait_for_completion_timeout(&sched->pause_comp,
+				msecs_to_jiffies(100));
+		if (!ret) {
+			mutex_unlock(&sched->m_reconf);
+			pr_err("Previous clock pause did not finish");
+			return -ETIMEDOUT;
+		}
+		ret = 0;
+		/**
+		 * Slimbus framework will call controller wakeup
+		 * Controller should make sure that it sets active framer
+		 * out of clock pause
+		 */
+		if (sched->clk_state == SLIM_CLK_PAUSED && ctrl->wakeup)
+			ret = ctrl->wakeup(ctrl);
+		if (!ret)
+			sched->clk_state = SLIM_CLK_ACTIVE;
+		mutex_unlock(&sched->m_reconf);
+		return ret;
+	}
+
+	/* already paused */
+	if (ctrl->sched.clk_state == SLIM_CLK_PAUSED) {
+		mutex_unlock(&sched->m_reconf);
+		return 0;
+	}
+
+	spin_lock_irqsave(&ctrl->txn_lock, flags);
+	for (i = 0; i < ctrl->last_tid; i++) {
+		/* Pending response for a message */
+		if (ctrl->txnt[i]) {
+			spin_unlock_irqrestore(&ctrl->txn_lock, flags);
+			mutex_unlock(&sched->m_reconf);
+			return -EBUSY;
+		}
+	}
+	spin_unlock_irqrestore(&ctrl->txn_lock, flags);
+
+	sched->clk_state = SLIM_CLK_ENTERING_PAUSE;
+
+	/* clock pause sequence */
+	ret = slim_processtxn(ctrl, &txn);
+	if (ret)
+		goto clk_pause_ret;
+
+	txn.mc = SLIM_MSG_MC_NEXT_PAUSE_CLOCK;
+	txn.rl = 4;
+	msg.num_bytes = 1;
+	msg.wbuf = &restart;
+	ret = slim_processtxn(ctrl, &txn);
+	if (ret)
+		goto clk_pause_ret;
+
+	txn.mc = SLIM_MSG_MC_RECONFIGURE_NOW;
+	txn.rl = 3;
+	msg.num_bytes = 1;
+	msg.wbuf = NULL;
+	ret = slim_processtxn(ctrl, &txn);
+
+clk_pause_ret:
+	if (ret) {
+		sched->clk_state = SLIM_CLK_ACTIVE;
+	} else {
+		sched->clk_state = SLIM_CLK_PAUSED;
+		complete(&sched->pause_comp);
+	}
+	mutex_unlock(&sched->m_reconf);
+	return ret;
+}
+EXPORT_SYMBOL(slim_ctrl_clk_pause);
+
 MODULE_LICENSE("GPL v2");
 MODULE_VERSION("0.1");
 MODULE_DESCRIPTION("Slimbus module");
diff --git a/include/linux/slimbus.h b/include/linux/slimbus.h
index 924cdd3..f1099c5 100644
--- a/include/linux/slimbus.h
+++ b/include/linux/slimbus.h
@@ -114,11 +114,21 @@ struct slim_addrt {
 #define SLIM_MSG_MC_REPLY_VALUE                  0x64
 #define SLIM_MSG_MC_CHANGE_VALUE                 0x68
 
+/* Clock pause Reconfiguration messages */
+#define SLIM_MSG_MC_BEGIN_RECONFIGURATION        0x40
+#define SLIM_MSG_MC_NEXT_PAUSE_CLOCK             0x4A
+#define SLIM_MSG_MC_RECONFIGURE_NOW              0x5F
+
 /* Destination type Values */
 #define SLIM_MSG_DEST_LOGICALADDR	0
 #define SLIM_MSG_DEST_ENUMADDR		1
 #define	SLIM_MSG_DEST_BROADCAST		3
 
+/* Clock pause values per slimbus spec */
+#define SLIM_CLK_FAST				0
+#define SLIM_CLK_CONST_PHASE			1
+#define SLIM_CLK_UNSPECIFIED			2
+
 /**
  * struct slim_val_inf: Slimbus value or information element
  * @start_offset: Specifies starting offset in information/value element map
@@ -163,6 +173,39 @@ struct slim_msg_txn {
 };
 
 /**
+ * enum slim_clk_state: Slimbus controller's clock state used internally for
+ *	maintaining current clock state.
+ * @SLIM_CLK_ACTIVE: Slimbus clock is active
+ * @SLIM_CLK_ENTERING_PAUSE: Slimbus clock pause sequence is being sent on the
+ *	bus. If this succeeds, state changes to SLIM_CLK_PAUSED. If the
+ *	transition fails, state changes back to SLIM_CLK_ACTIVE
+ * @SLIM_CLK_PAUSED: Slimbus controller clock has paused.
+ */
+enum slim_clk_state {
+	SLIM_CLK_ACTIVE,
+	SLIM_CLK_ENTERING_PAUSE,
+	SLIM_CLK_PAUSED,
+};
+
+/**
+ * struct slim_sched: Framework uses this structure internally for scheduling.
+ * @clk_state: Controller's clock state from enum slim_clk_state
+ * @pause_comp: Signals completion of clock pause sequence. This is useful when
+ *	client tries to call slimbus transaction when controller is entering
+ *	clock pause.
+ * @m_reconf: This mutex is held until current reconfiguration (data channel
+ *	scheduling, message bandwidth reservation) is done. Message APIs can
+ *	use the bus concurrently when this mutex is held since elemental access
+ *	messages can be sent on the bus when reconfiguration is in progress.
+ */
+struct slim_sched {
+	int			clkgear;
+	enum slim_clk_state	clk_state;
+	struct completion	pause_comp;
+	struct mutex		m_reconf;
+};
+
+/**
  * struct slim_controller: Controls every instance of SLIMbus
  *				(similar to 'master' on SPI)
  *	'Manager device' is responsible for  device management, bandwidth
@@ -200,6 +243,7 @@ struct slim_msg_txn {
  * @txnt: Table of transactions having transaction ID
  * @txn_lock: Lock to protect table of transactions
  * @last_tid: size of the table txnt (can't grow beyond 256 since TID is 8-bits)
+ * @sched: scheduler structure used by the controller
  * @dev_released: completion used to signal when sysfs has released this
  *	controller so that it can be deleted during shutdown
  * @xfer_msg: Transfer a message on this controller (this can be a broadcast
@@ -211,6 +255,9 @@ struct slim_msg_txn {
  * @get_laddr: It is possible that controller needs to set fixed logical
  *	address table and get_laddr can be used in that case so that controller
  *	can do this assignment.
+ * @wakeup: This function pointer implements controller-specific procedure
+ *	to wake it up from clock-pause. Framework will call this to bring
+ *	the controller out of clock pause.
  */
 struct slim_controller {
 	struct device		dev;
@@ -229,6 +276,7 @@ struct slim_controller {
 	struct slim_val_inf	*txnt[SLIM_MAX_TXNS];
 	u8			last_tid;
 	spinlock_t		txn_lock;
+	struct slim_sched	sched;
 	struct completion	dev_released;
 	int			(*xfer_msg)(struct slim_controller *ctrl,
 				struct slim_msg_txn *txn);
@@ -236,6 +284,7 @@ struct slim_controller {
 					     struct slim_eaddr *ea, u8 laddr);
 	int			(*get_laddr)(struct slim_controller *ctrl,
 					     struct slim_eaddr *ea, u8 *laddr);
+	int			(*wakeup)(struct slim_controller *ctrl);
 };
 
 #define to_slim_controller(d) container_of(d, struct slim_controller, dev)
@@ -521,4 +570,20 @@ static inline bool slim_tid_txn(u8 mt, u8 mc)
 }
 /* end of message apis */
 
+/**
+ * slim_ctrl_clk_pause: Called by slimbus controller to enter/exit 'clock pause'
+ * Slimbus specification needs this sequence to turn-off clocks for the bus.
+ * The sequence involves sending 3 broadcast messages (reconfiguration
+ * sequence) to inform all devices on the bus.
+ * To exit clock-pause, controller typically wakes up active framer device.
+ * @ctrl: controller requesting bus to be paused or woken up
+ * @wakeup: Wakeup this controller from clock pause.
+ * @restart: Restart time value per spec used for clock pause. This value
+ *	isn't used when controller is to be woken up.
+ * This API executes clock pause reconfiguration sequence if wakeup is false.
+ * If wakeup is true, controller's wakeup is called.
+ * For entering clock-pause, -EBUSY is returned if a message txn in pending.
+ */
+int slim_ctrl_clk_pause(struct slim_controller *ctrl, bool wakeup, u8 restart);
+
 #endif /* _LINUX_SLIMBUS_H */
-- 
1.8.2.1

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