From: Stefan Eichenberger <stefan.eichenberger@toradex.com>

According to the i.MX8M Mini reference manual chapter "16.1.4.2
Generation of Start" it is only necessary to poll for bus busy and
arbitration lost in multi master mode. This helps to avoid rescheduling
while the i2c bus is busy and avoids SMBus devices to timeout. For
backward compatibility, the single-master property needs to be
explicitly set to disable the bus busy polling.

Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
@Frank and Oleksij: I kept your tags even though I made multi-master the
new default. Let me know if you have any objections.

 drivers/i2c/busses/i2c-imx.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index 98539313cbc97..d697abd2459d4 100644
--- a/drivers/i2c/busses/i2c-imx.c
+++ b/drivers/i2c/busses/i2c-imx.c
@@ -216,6 +216,8 @@ struct imx_i2c_struct {
 	struct i2c_client	*slave;
 	enum i2c_slave_event last_slave_event;
 
+	bool			multi_master;
+
 	/* For checking slave events. */
 	spinlock_t     slave_lock;
 	struct hrtimer slave_timer;
@@ -481,6 +483,9 @@ static int i2c_imx_bus_busy(struct imx_i2c_struct *i2c_imx, int for_busy, bool a
 	unsigned long orig_jiffies = jiffies;
 	unsigned int temp;
 
+	if (!i2c_imx->multi_master)
+		return 0;
+
 	while (1) {
 		temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2SR);
 
@@ -540,8 +545,8 @@ static int i2c_imx_trx_complete(struct imx_i2c_struct *i2c_imx, bool atomic)
 		return -ETIMEDOUT;
 	}
 
-	/* check for arbitration lost */
-	if (i2c_imx->i2csr & I2SR_IAL) {
+	/* In multi-master mode check for arbitration lost */
+	if (i2c_imx->multi_master && (i2c_imx->i2csr & I2SR_IAL)) {
 		dev_dbg(&i2c_imx->adapter.dev, "<%s> Arbitration lost\n", __func__);
 		i2c_imx_clear_irq(i2c_imx, I2SR_IAL);
 
@@ -1468,6 +1473,12 @@ static int i2c_imx_probe(struct platform_device *pdev)
 		goto rpm_disable;
 	}
 
+	/*
+	 * We use the single-master property for backward compatibility.
+	 * By default multi master mode is enabled.
+	 */
+	i2c_imx->multi_master = !of_property_read_bool(pdev->dev.of_node, "single-master");
+
 	/* Set up clock divider */
 	i2c_imx->bitrate = I2C_MAX_STANDARD_MODE_FREQ;
 	ret = of_property_read_u32(pdev->dev.of_node,
-- 
2.43.0