Patch "i2c: testunit: on errors, repeat NACK until STOP" has been added to the 6.12-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    i2c: testunit: on errors, repeat NACK until STOP

to the 6.12-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     i2c-testunit-on-errors-repeat-nack-until-stop.patch
and it can be found in the queue-6.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit b21d0350d84581fa3c9c80f84bffb8a2bfe634f7
Author: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
Date:   Wed Jan 15 17:23:47 2025 +0100

    i2c: testunit: on errors, repeat NACK until STOP
    
    [ Upstream commit 6ad30f7890423341f4b79329af1f9b9bb3cdec03 ]
    
    This backend requests a NACK from the controller driver when it detects
    an error. If that request gets ignored from some reason, subsequent
    accesses will wrongly be handled OK. To fix this, an error now changes
    the state machine, so the backend will report NACK until a STOP
    condition has been detected. This make the driver more robust against
    controllers which will sadly apply the NACK not to the current byte but
    the next one.
    
    Fixes: a8335c64c5f0 ("i2c: add slave testunit driver")
    Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/i2c/i2c-slave-testunit.c b/drivers/i2c/i2c-slave-testunit.c
index 9fe3150378e86..7ae0c7902f670 100644
--- a/drivers/i2c/i2c-slave-testunit.c
+++ b/drivers/i2c/i2c-slave-testunit.c
@@ -38,6 +38,7 @@ enum testunit_regs {
 
 enum testunit_flags {
 	TU_FLAG_IN_PROCESS,
+	TU_FLAG_NACK,
 };
 
 struct testunit_data {
@@ -90,8 +91,10 @@ static int i2c_slave_testunit_slave_cb(struct i2c_client *client,
 
 	switch (event) {
 	case I2C_SLAVE_WRITE_REQUESTED:
-		if (test_bit(TU_FLAG_IN_PROCESS, &tu->flags))
-			return -EBUSY;
+		if (test_bit(TU_FLAG_IN_PROCESS | TU_FLAG_NACK, &tu->flags)) {
+			ret = -EBUSY;
+			break;
+		}
 
 		memset(tu->regs, 0, TU_NUM_REGS);
 		tu->reg_idx = 0;
@@ -99,8 +102,10 @@ static int i2c_slave_testunit_slave_cb(struct i2c_client *client,
 		break;
 
 	case I2C_SLAVE_WRITE_RECEIVED:
-		if (test_bit(TU_FLAG_IN_PROCESS, &tu->flags))
-			return -EBUSY;
+		if (test_bit(TU_FLAG_IN_PROCESS | TU_FLAG_NACK, &tu->flags)) {
+			ret = -EBUSY;
+			break;
+		}
 
 		if (tu->reg_idx < TU_NUM_REGS)
 			tu->regs[tu->reg_idx] = *val;
@@ -129,6 +134,8 @@ static int i2c_slave_testunit_slave_cb(struct i2c_client *client,
 		 * here because we still need them in the workqueue!
 		 */
 		tu->reg_idx = 0;
+
+		clear_bit(TU_FLAG_NACK, &tu->flags);
 		break;
 
 	case I2C_SLAVE_READ_PROCESSED:
@@ -151,6 +158,10 @@ static int i2c_slave_testunit_slave_cb(struct i2c_client *client,
 		break;
 	}
 
+	/* If an error occurred somewhen, we NACK everything until next STOP */
+	if (ret)
+		set_bit(TU_FLAG_NACK, &tu->flags);
+
 	return ret;
 }