[PATCH] i2c: testunit: on errors, repeat NACK until STOP

[PATCH] i2c: testunit: on errors, repeat NACK until STOP

[Wolfram Sang]

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@sang-engineering.com>
---

Found, debugged, and tested on a Renesas Lager board (R-Car H2).

 drivers/i2c/i2c-slave-testunit.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/i2c-slave-testunit.c b/drivers/i2c/i2c-slave-testunit.c
index 0d6fbaa48248..6de4307050dd 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;
 }
 
-- 
2.45.2

Re: [PATCH] i2c: testunit: on errors, repeat NACK until STOP

[Wolfram Sang]

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On Wed, Jan 15, 2025 at 07:45:52PM +0100, Wolfram Sang wrote:
> 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@sang-engineering.com>

Applied to for-current, thanks!


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