i2c: testunit: discard write requests while old command is running

BugLink: https://bugs.launchpad.net/bugs/2076435

[ Upstream commit c116deafd1a5cc1e9739099eb32114e90623209c ]

When clearing registers on new write requests was added, the protection
for currently running commands was missed leading to concurrent access
to the testunit registers. Check the flag beforehand.

Fixes: b39ab96 ("i2c: testunit: add support for block process calls")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Portia Stephens <portia.stephens@canonical.com>
Signed-off-by: Roxana Nicolescu <roxana.nicolescu@canonical.com>

Author: Wolfram Sang

drivers/i2c/i2c-slave-testunit.c

@@ -121,6 +121,9 @@ static int i2c_slave_testunit_slave_cb(struct i2c_client *client,
 		break;
 
 	case I2C_SLAVE_WRITE_REQUESTED:
+		if (test_bit(TU_FLAG_IN_PROCESS, &tu->flags))
+			return -EBUSY;
+
 		memset(tu->regs, 0, TU_NUM_REGS);
 		tu->reg_idx = 0;
 		break;