[PATCH 2/2] i2c: designware: Abort stuck master when disabling times out

[Sarah Maedel <sarah.maedel@hetzner-cloud.de>]

__i2c_dw_disable() only aborts the current transfer if MST_ON_HOLD or
MASTER_HOLD_TX_FIFO_EMPTY is set. These bits only exist with
IC_STAT_FOR_CLK_STRETCH, so on other configurations a master left
holding the bus can't be disabled: IC_ENABLE_STATUS stays set and
IC_STATUS keeps reporting MST_ACTIVITY.

If the master is still active once the disable loop has timed out,
abort the transfer and try again. Also disable the adapter from
i2c_dw_wait_bus_not_busy() when bus recovery didn't help, so the next
transfer recovers the controller.

Tested on Ampere Altra by putting the controller into this state
through /dev/mem (a write without STOP, then clearing IC_ENABLE).

Signed-off-by: Sarah Maedel <sarah.maedel@hetzner-cloud.de>
---
 drivers/i2c/busses/i2c-designware-common.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/i2c/busses/i2c-designware-common.c b/drivers/i2c/busses/i2c-designware-common.c
index a1eca6cd4b75..2e8de0f6c1ed 100644
--- a/drivers/i2c/busses/i2c-designware-common.c
+++ b/drivers/i2c/busses/i2c-designware-common.c
@@ -643,6 +643,7 @@ void __i2c_dw_disable(struct dw_i2c_dev *dev)
 	if (dev->mode == DW_IC_SLAVE && (ic_stats & DW_IC_STATUS_SLAVE_ACTIVITY))
 		abort_needed = true;
 
+retry:
 	if (abort_needed) {
 		if (!(enable & DW_IC_ENABLE_ENABLE)) {
 			regmap_write(dev->map, DW_IC_ENABLE, DW_IC_ENABLE_ENABLE);
@@ -684,6 +685,19 @@ void __i2c_dw_disable(struct dw_i2c_dev *dev)
 		usleep_range(25, 250);
 	} while (timeout--);
 
+	/*
+	 * Without IC_STAT_FOR_CLK_STRETCH the hold status bits above don't
+	 * exist, so a stuck master is only noticed here.
+	 */
+	regmap_read(dev->map, DW_IC_STATUS, &ic_stats);
+	if (!abort_needed && (ic_stats & DW_IC_STATUS_MASTER_ACTIVITY)) {
+		dev_warn(dev->dev, "controller stuck active, aborting\n");
+		regmap_read(dev->map, DW_IC_ENABLE, &enable);
+		abort_needed = true;
+		timeout = 100;
+		goto retry;
+	}
+
 	dev_warn(dev->dev, "timeout in disabling adapter\n");
 }
 
@@ -764,6 +778,11 @@ int i2c_dw_wait_bus_not_busy(struct dw_i2c_dev *dev)
 		i2c_recover_bus(&dev->adapter);
 
 		regmap_read(dev->map, DW_IC_STATUS, &status);
+		if (status & DW_IC_STATUS_MASTER_ACTIVITY) {
+			/* Disabling aborts a master stuck on the bus */
+			__i2c_dw_disable(dev);
+			regmap_read(dev->map, DW_IC_STATUS, &status);
+		}
 		if (!(status & DW_IC_STATUS_ACTIVITY))
 			ret = 0;
 	}
-- 
2.47.3