[PATCH v3 4/4] i2c: designware: Handle active slave cleanly

William A. Kennington III
2026-05-04T20:15:07Z

When the I2C master attempts a new transaction while the slave
controller is shutting down or restarting, it can lead to bus lockups
and system bootloops if the hardware enters an inconsistent state.

Address this by ensuring that the internal state machines are properly
cleared when disabling the controller if slave activity is detected.

If the controller remains active after disabling, perform a bus recovery
to reset it to a known good state.

Signed-off-by: William A. Kennington III <william@wkennington.com>
---
drivers/i2c/busses/i2c-designware-common.c | 8 ++++++++
drivers/i2c/busses/i2c-designware-core.h | 4 ++--
drivers/i2c/busses/i2c-designware-master.c | 31 ++++++++++++++++++------------
3 files changed, 29 insertions(+), 14 deletions(-)

diff --git a/drivers/i2c/busses/i2c-designware-common.c b/drivers/i2c/busses/i2c-designware-common.c
index 0703fb29038c..31394d8fe612 100644
--- a/drivers/i2c/busses/i2c-designware-common.c
+++ b/drivers/i2c/busses/i2c-designware-common.c
@@ -633,6 +633,14 @@ void __i2c_dw_disable(struct dw_i2c_dev *dev)

abort_needed = (raw_intr_stats & DW_IC_INTR_MST_ON_HOLD) ||
(ic_stats & DW_IC_STATUS_MASTER_HOLD_TX_FIFO_EMPTY);
+
+ /*
+ * If we are in slave mode and there is activity, we should also
+ * trigger an abort to clear the internal state machines.
+ */
+ if (dev->mode == DW_IC_SLAVE && (ic_stats & DW_IC_STATUS_SLAVE_ACTIVITY))
+ abort_needed = true;
+
if (abort_needed) {
if (!(enable & DW_IC_ENABLE_ENABLE)) {
regmap_write(dev->map, DW_IC_ENABLE, DW_IC_ENABLE_ENABLE);
diff --git a/drivers/i2c/busses/i2c-designware-core.h b/drivers/i2c/busses/i2c-designware-core.h
index 8b422249acbd..259b7ce16d0c 100644
--- a/drivers/i2c/busses/i2c-designware-core.h
+++ b/drivers/i2c/busses/i2c-designware-core.h
@@ -129,8 +129,8 @@
#define DW_IC_STATUS_ACTIVITY BIT(0)
#define DW_IC_STATUS_TFE BIT(2)
#define DW_IC_STATUS_RFNE BIT(3)
-#define DW_IC_STATUS_MASTER_ACTIVITY BIT(5)
-#define DW_IC_STATUS_SLAVE_ACTIVITY BIT(6)
+#define DW_IC_STATUS_MASTER_ACTIVITY BIT(5)
+#define DW_IC_STATUS_SLAVE_ACTIVITY BIT(6)
#define DW_IC_STATUS_MASTER_HOLD_TX_FIFO_EMPTY BIT(7)

#define DW_IC_SDA_HOLD_RX_SHIFT 16
diff --git a/drivers/i2c/busses/i2c-designware-master.c b/drivers/i2c/busses/i2c-designware-master.c
index de929b91d5ea..7a301c8b604e 100644
--- a/drivers/i2c/busses/i2c-designware-master.c
+++ b/drivers/i2c/busses/i2c-designware-master.c
@@ -785,18 +785,25 @@ __i2c_dw_xfer_one_part(struct dw_i2c_dev *dev, struct i2c_msg *msgs, size_t num)
* IC_RAW_INTR_STAT.MASTER_ON_HOLD holding SCL low. Check if
* controller is still ACTIVE before disabling I2C.
*/
- if (i2c_dw_is_controller_active(dev))
- dev_err(dev->dev, "controller active\n");
-
- /*
- * We must disable the adapter before returning and signaling the end
- * of the current transfer. Otherwise the hardware might continue
- * generating interrupts which in turn causes a race condition with
- * the following transfer. Needs some more investigation if the
- * additional interrupts are a hardware bug or this driver doesn't
- * handle them correctly yet.
- */
- __i2c_dw_disable_nowait(dev);
+ if (i2c_dw_is_controller_active(dev)) {
+ /*
+ * If the controller is still active after the timeout, attempt a
+ * bus recovery to clear any potentially locked state.
+ */
+ dev_err(dev->dev, "controller active after xfer, recovering\n");
+ i2c_recover_bus(&dev->adapter);
+ i2c_dw_init(dev);
+ } else {
+ /*
+ * We must disable the adapter before returning and signaling the end
+ * of the current transfer. Otherwise the hardware might continue
+ * generating interrupts which in turn causes a race condition with
+ * the following transfer. Needs some more investigation if the
+ * additional interrupts are a hardware bug or this driver doesn't
+ * handle them correctly yet.
+ */
+ __i2c_dw_disable_nowait(dev);
+ }

if (dev->msg_err)
return dev->msg_err;

--
2.54.0.545.g6539524ca2-goog