[RFC PATCH i2c-next 2/2] i2c: aspeed: Add bus idle waiting logic for multi-master use cases

[Jae Hyun Yoo]

In multi-master environment, this driver side master cannot know
exactly when peer master sends data to this side master so a case
can be happened that this master tries to send data through the
master_xfer function but slave data from peer master is still
being processed by this driver.

To prevent state corruption in the case, this patch adds checking
if any slave operation is ongoing and it wait up to the timeout
duration before starting a master_xfer operation.

Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@xxxxxxxxxxxxxxx>
---
 drivers/i2c/busses/i2c-aspeed.c | 70 ++++++++++++++++++++++++++-------
 1 file changed, 55 insertions(+), 15 deletions(-)

diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
index c258c4d9a4c0..73359eda98be 100644
--- a/drivers/i2c/busses/i2c-aspeed.c
+++ b/drivers/i2c/busses/i2c-aspeed.c
@@ -12,6 +12,7 @@
 
 #include <linux/clk.h>
 #include <linux/completion.h>
+#include <linux/delay.h>
 #include <linux/err.h>
 #include <linux/errno.h>
 #include <linux/i2c.h>
@@ -99,6 +100,7 @@
 		 ASPEED_I2CD_INTR_TX_ACK)
 
 /* 0x14 : I2CD Command/Status Register   */
+#define ASPEED_I2CD_XFER_MODE_STS_MASK			GENMASK(22, 19)
 #define ASPEED_I2CD_SCL_LINE_STS			BIT(18)
 #define ASPEED_I2CD_SDA_LINE_STS			BIT(17)
 #define ASPEED_I2CD_BUS_BUSY_STS			BIT(16)
@@ -115,6 +117,10 @@
 /* 0x18 : I2CD Slave Device Address Register   */
 #define ASPEED_I2CD_DEV_ADDR_MASK			GENMASK(6, 0)
 
+/* Timeout for bus busy checking */
+#define ASPEED_I2CD_IDLE_WAIT_TIMEOUT_MS_DEFAULT	100   /* 100 ms */
+#define ASPEED_I2CD_BUS_BUSY_CHECK_INTERVAL_US		10000 /* 10 ms */
+
 enum aspeed_i2c_master_state {
 	ASPEED_I2C_MASTER_INACTIVE,
 	ASPEED_I2C_MASTER_START,
@@ -155,6 +161,9 @@ struct aspeed_i2c_bus {
 	int				cmd_err;
 	/* Protected only by i2c_lock_bus */
 	int				master_xfer_result;
+	/* Multi-master */
+	bool				multi_master;
+	u32				idle_wait_timeout_ms;
 #if IS_ENABLED(CONFIG_I2C_SLAVE)
 	struct i2c_client		*slave;
 	enum aspeed_i2c_slave_state	slave_state;
@@ -590,27 +599,49 @@ static irqreturn_t aspeed_i2c_bus_irq(int irq, void *dev_id)
 	return irq_remaining ? IRQ_NONE : IRQ_HANDLED;
 }
 
+static int aspeed_i2c_check_bus_busy(struct aspeed_i2c_bus *bus)
+{
+	u32 status_check_mask = ASPEED_I2CD_BUS_BUSY_STS;
+	ktime_t timeout;
+
+	if (bus->multi_master) {
+		might_sleep();
+		timeout = ktime_add_ms(ktime_get(), bus->idle_wait_timeout_ms);
+		/*
+		 * ASPEED_I2CD_XFER_MODE_STS_MASK is marked as
+		 * 'for debugging purpose only' in datasheet but ASPEED
+		 * confirmed that this reflects real information and good to be
+		 * used in practical code. It will be used only in multi-master
+		 * use cases.
+		 */
+		status_check_mask |= ASPEED_I2CD_XFER_MODE_STS_MASK;
+	}
+
+	for (;;) {
+		if (!(readl(bus->base + ASPEED_I2C_CMD_REG) &
+		      status_check_mask))
+			return 0;
+		if (!bus->multi_master)
+			break;
+		if (ktime_compare(ktime_get(), timeout) > 0)
+			break;
+		usleep_range((ASPEED_I2CD_BUS_BUSY_CHECK_INTERVAL_US >> 2) + 1,
+			     ASPEED_I2CD_BUS_BUSY_CHECK_INTERVAL_US);
+	}
+
+	return aspeed_i2c_recover_bus(bus);
+}
+
 static int aspeed_i2c_master_xfer(struct i2c_adapter *adap,
 				  struct i2c_msg *msgs, int num)
 {
 	struct aspeed_i2c_bus *bus = i2c_get_adapdata(adap);
 	unsigned long time_left, flags;
-	int ret = 0;
-
-	spin_lock_irqsave(&bus->lock, flags);
-	bus->cmd_err = 0;
 
-	/* If bus is busy, attempt recovery. We assume a single master
-	 * environment.
-	 */
-	if (readl(bus->base + ASPEED_I2C_CMD_REG) & ASPEED_I2CD_BUS_BUSY_STS) {
-		spin_unlock_irqrestore(&bus->lock, flags);
-		ret = aspeed_i2c_recover_bus(bus);
-		if (ret)
-			return ret;
-		spin_lock_irqsave(&bus->lock, flags);
-	}
+	if (aspeed_i2c_check_bus_busy(bus))
+		return -EAGAIN;
 
+	spin_lock_irqsave(&bus->lock, flags);
 	bus->cmd_err = 0;
 	bus->msgs = msgs;
 	bus->msgs_index = 0;
@@ -798,8 +829,17 @@ static int aspeed_i2c_init(struct aspeed_i2c_bus *bus,
 	if (ret < 0)
 		return ret;
 
-	if (!of_property_read_bool(pdev->dev.of_node, "multi-master"))
+	if (of_property_read_bool(pdev->dev.of_node, "multi-master")) {
+		bus->multi_master = true;
+		ret = of_property_read_u32(pdev->dev.of_node,
+					   "idle-wait-timeout-ms",
+					   &bus->idle_wait_timeout_ms);
+		if (ret)
+			bus->idle_wait_timeout_ms =
+				ASPEED_I2CD_IDLE_WAIT_TIMEOUT_MS_DEFAULT;
+	} else {
 		fun_ctrl_reg |= ASPEED_I2CD_MULTI_MASTER_DIS;
+	}
 
 	/* Enable Master Mode */
 	writel(readl(bus->base + ASPEED_I2C_FUN_CTRL_REG) | fun_ctrl_reg,
-- 
2.18.0