[PATCH i2c-next v4 3/3] i2c: aspeed: Add bus idle waiting logic for multi-master use cases

[Jae Hyun Yoo]

In multi-master environment, this driver's master cannot know
exactly when peer master sends data to this driver's slave 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
code if any slave operation is ongoing and it waits up to the
timeout duration before starting a master_xfer operation. Since
the BUSY bit in the I2CD14 register doesn't cover the whole slave
sequence, it uses 'Transfer Mode State Machine' bit fields to
make up the problem of the BUSY bit.

Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo at linux.intel.com>
---
 drivers/i2c/busses/i2c-aspeed.c | 62 +++++++++++++++++++++++++--------
 1 file changed, 47 insertions(+), 15 deletions(-)

diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
index 6d31f54a6653..edb1944c867b 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 +117,9 @@
 /* 0x18 : I2CD Slave Device Address Register   */
 #define ASPEED_I2CD_DEV_ADDR_MASK			GENMASK(6, 0)
 
+/* Busy checking */
+#define ASPEED_I2C_BUS_BUSY_CHECK_INTERVAL_US		(10 * 1000)
+
 enum aspeed_i2c_master_state {
 	ASPEED_I2C_MASTER_INACTIVE,
 	ASPEED_I2C_MASTER_START,
@@ -156,6 +161,8 @@ struct aspeed_i2c_bus {
 	int				cmd_err;
 	/* Protected only by i2c_lock_bus */
 	int				master_xfer_result;
+	/* Multi-master */
+	bool				multi_master;
 #if IS_ENABLED(CONFIG_I2C_SLAVE)
 	struct i2c_client		*slave;
 	enum aspeed_i2c_slave_state	slave_state;
@@ -596,27 +603,50 @@ 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(),
+				       jiffies_to_msecs(bus->adap.timeout));
+		/*
+		 * 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_I2C_BUS_BUSY_CHECK_INTERVAL_US >> 2) + 1,
+			     ASPEED_I2C_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;
@@ -827,7 +857,9 @@ 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;
+	else
 		fun_ctrl_reg |= ASPEED_I2CD_MULTI_MASTER_DIS;
 
 	/* Enable Master Mode */
-- 
2.19.0