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[1/1] i2c: designware: Ensure runtime suspend is invoked during rapid slave unregistration and registration

Message ID 20250412023303.378600-1-ende.tan@starfivetech.com
State New
Headers show
Series [1/1] i2c: designware: Ensure runtime suspend is invoked during rapid slave unregistration and registration | expand

Commit Message

EnDe Tan April 12, 2025, 2:33 a.m. UTC 
From: Tan En De <ende.tan@starfivetech.com>

Replaced pm_runtime_put() with pm_runtime_put_sync_suspend() to ensure
the runtime suspend is invoked immediately when unregistering a slave.
This prevents a race condition where suspend was skipped when
unregistering and registering slave in quick succession.

Signed-off-by: Tan En De <ende.tan@starfivetech.com>
---
 drivers/i2c/busses/i2c-designware-slave.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

EnDe Tan April 20, 2025, 3:31 a.m. UTC | #1 
It appears that when performing a rapid sequence of `delete_device -> new_device -> delete_device -> new_device`, the `dw_i2c_plat_runtime_suspend` is not invoked for the second `delete_device`.

This seems to happen because when `i2c_dw_unreg_slave` is about to trigger suspend during the second `delete_device`, the second `new_device` operation cancels the suspend. As a result, `dw_i2c_plat_runtime_resume` is not called (since there was no suspend), which means `i_dev->init` (i.e., `i2c_dw_init_slave`) is skipped.

Because `i2c_dw_init_slave` is skipped, `i2c_dw_configure_fifo_slave` is not invoked, which leaves `DW_IC_INTR_MASK` unconfigured.
If we inspect the interrupt mask register using devmem, it will show as zero.

Here's an example shell script to reproduce the issue:
```
#!/bin/sh

SLAVE_LADDR=0x1010
SLAVE_BUS=13
NEW_DEVICE=/sys/bus/i2c/devices/i2c-$SLAVE_BUS/new_device
DELETE_DEVICE=/sys/bus/i2c/devices/i2c-$SLAVE_BUS/delete_device

# Create initial device
echo slave-24c02 $SLAVE_LADDR > $NEW_DEVICE
sleep 2

# Rapid sequence of delete_device -> new_device -> delete_device -> new_device
echo $SLAVE_LADDR > $DELETE_DEVICE
echo slave-24c02 $SLAVE_LADDR > $NEW_DEVICE
echo $SLAVE_LADDR > $DELETE_DEVICE
echo slave-24c02 $SLAVE_LADDR > $NEW_DEVICE

# If we use devmem to inspect IC_INTR_MASK, it will show as zero
```
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Patch

diff --git a/drivers/i2c/busses/i2c-designware-slave.c b/drivers/i2c/busses/i2c-designware-slave.c
index 5cd4a5f7a472..b936a240db0a 100644
--- a/drivers/i2c/busses/i2c-designware-slave.c
+++ b/drivers/i2c/busses/i2c-designware-slave.c
@@ -96,7 +96,7 @@  static int i2c_dw_unreg_slave(struct i2c_client *slave)
 	i2c_dw_disable(dev);
 	synchronize_irq(dev->irq);
 	dev->slave = NULL;
-	pm_runtime_put(dev->dev);
+	pm_runtime_put_sync_suspend(dev->dev);
 
 	return 0;
 }