[PATCH 1/1] i2c: tegra: fix error handling in tegra_i2c_xfer()

[Saurav Sachidanand <sauravsc@amazon.com>]

Fix two bugs in the SW mutex path introduced by commit 6077cfd716fb
("i2c: tegra: Add support for SW mutex register"):

1. If tegra_i2c_mutex_lock() fails, the function returns without calling
   pm_runtime_put(), leaking the runtime PM reference acquired by the
   preceding pm_runtime_get_sync(). Add the missing pm_runtime_put()
   before returning.

2. tegra_i2c_mutex_unlock() unconditionally overwrites ret, which may
   already hold a transfer error from tegra_i2c_xfer_msg(). If the
   transfer failed but the unlock succeeds, the error is silently lost
   and the function incorrectly reports success. Use a separate variable
   for the unlock return value and preserve error priority:
   transfer error > unlock error > message count.

Fixes: 6077cfd716fb ("i2c: tegra: Add support for SW mutex register")
Signed-off-by: Saurav Sachidanand <sauravsc@amazon.com>
---
 drivers/i2c/busses/i2c-tegra.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
index 9fd5ade774a0b..704942d10d69d 100644
--- a/drivers/i2c/busses/i2c-tegra.c
+++ b/drivers/i2c/busses/i2c-tegra.c
@@ -1656,7 +1656,7 @@ static int tegra_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
 			  int num)
 {
 	struct tegra_i2c_dev *i2c_dev = i2c_get_adapdata(adap);
-	int i, ret;
+	int i, ret, ret2;
 
 	ret = pm_runtime_get_sync(i2c_dev->dev);
 	if (ret < 0) {
@@ -1666,8 +1666,10 @@ static int tegra_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
 	}
 
 	ret = tegra_i2c_mutex_lock(i2c_dev);
-	if (ret)
+	if (ret) {
+		pm_runtime_put(i2c_dev->dev);
 		return ret;
+	}
 
 	for (i = 0; i < num; i++) {
 		enum msg_end_type end_type = MSG_END_STOP;
@@ -1698,10 +1700,10 @@ static int tegra_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[],
 			break;
 	}
 
-	ret = tegra_i2c_mutex_unlock(i2c_dev);
+	ret2 = tegra_i2c_mutex_unlock(i2c_dev);
 	pm_runtime_put(i2c_dev->dev);
 
-	return ret ?: i;
+	return ret ?: ret2 ?: i;
 }
 
 static int tegra_i2c_xfer_atomic(struct i2c_adapter *adap,
-- 
2.47.3