* [PATCH 1/2] i2c: designware: Only check for spurious STOP without EMPTYFIFO_HOLD_MASTER
2026-11-10 15:43 [PATCH 0/2] i2c: designware: Fix stuck master on multi-master buses Sarah Maedel
@ 2026-11-10 15:43 ` Sarah Maedel
2026-11-10 15:43 ` [PATCH 2/2] i2c: designware: Abort stuck master when disabling times out Sarah Maedel
1 sibling, 0 replies; 3+ messages in thread
From: Sarah Maedel @ 2026-11-10 15:43 UTC (permalink / raw)
To: Mika Westerberg, Andi Shyti
Cc: Andy Shevchenko, Benoît Monin, David LaPorte, linux-i2c,
linux-kernel, stable
Commit 560072246088 ("i2c: designware: Support of controller with
IC_EMPTYFIFO_HOLD_MASTER disabled") fails a transfer when STOP_DET is
seen while a read or write is still in progress. This is meant to catch
Tx FIFO underruns on controllers without IC_EMPTYFIFO_HOLD_MASTER_EN,
but the check is applied to all controllers.
Controllers with IC_EMPTYFIFO_HOLD_MASTER_EN hold SCL on an empty Tx
FIFO and can't underrun, but on a multi-master bus they also see
STOP_DET for other masters' transactions. The driver then disables the
adapter while the controller is still busy with the transfer. On
DW_apb_i2c 1.20a (Ampere Altra, IPMI SSIF shared with the BMC) this
leaves the master stuck with IC_ENABLE_STATUS set, and all following
transfers fail with "timeout waiting for bus ready".
Limit the check to controllers without IC_EMPTYFIFO_HOLD_MASTER, as
suggested by David LaPorte.
Fixes: 560072246088 ("i2c: designware: Support of controller with IC_EMPTYFIFO_HOLD_MASTER disabled")
Cc: stable@vger.kernel.org # v7.0+
Suggested-by: David LaPorte <dalaport@amazon.com>
Link: https://lore.kernel.org/all/20260505232244.71807-1-dalaport@amazon.com/
Signed-off-by: Sarah Maedel <sarah.maedel@hetzner-cloud.de>
---
drivers/i2c/busses/i2c-designware-master.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/i2c/busses/i2c-designware-master.c b/drivers/i2c/busses/i2c-designware-master.c
index 7e1d9a2e7733..d7d99c7b6ef2 100644
--- a/drivers/i2c/busses/i2c-designware-master.c
+++ b/drivers/i2c/busses/i2c-designware-master.c
@@ -675,8 +675,11 @@ static void i2c_dw_process_transfer(struct dw_i2c_dev *dev, unsigned int stat)
if (stat & DW_IC_INTR_TX_EMPTY)
i2c_dw_xfer_msg(dev);
- /* Abort if we detect a STOP in the middle of a read or a write */
- if ((stat & DW_IC_INTR_STOP_DET) &&
+ /*
+ * Abort if we detect a STOP in the middle of a read or a write on a
+ * controller that doesn't hold SCL on an empty Tx FIFO.
+ */
+ if (!dev->emptyfifo_hold_master && (stat & DW_IC_INTR_STOP_DET) &&
(dev->status & (STATUS_READ_IN_PROGRESS | STATUS_WRITE_IN_PROGRESS))) {
dev_err(dev->dev, "spurious STOP detected\n");
dev->rx_outstanding = 0;
--
2.47.3
^ permalink raw reply [flat|nested] 3+ messages in thread* [PATCH 2/2] i2c: designware: Abort stuck master when disabling times out
2026-11-10 15:43 [PATCH 0/2] i2c: designware: Fix stuck master on multi-master buses Sarah Maedel
2026-11-10 15:43 ` [PATCH 1/2] i2c: designware: Only check for spurious STOP without EMPTYFIFO_HOLD_MASTER Sarah Maedel
@ 2026-11-10 15:43 ` Sarah Maedel
1 sibling, 0 replies; 3+ messages in thread
From: Sarah Maedel @ 2026-11-10 15:43 UTC (permalink / raw)
To: Mika Westerberg, Andi Shyti
Cc: Andy Shevchenko, Benoît Monin, David LaPorte, linux-i2c,
linux-kernel
__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
^ permalink raw reply [flat|nested] 3+ messages in thread