[PATCH v2] i2c: imx: Fix slave registration error path and missing timer cleanup

[Liem <liem16213@gmail.com>]

There are two issues that affect the i2c-imx slave handling:

1. In i2c_imx_reg_slave(), i2c_imx->slave is checked at the beginning
   and the function returns -EBUSY if it is non-NULL.  If
   pm_runtime_resume_and_get() fails later, the error path returns
   without clearing i2c_imx->slave, leaving it non-NULL.  Subsequent
   attempts to register a slave will then immediately fail with
   -EBUSY, making it impossible to register the slave again.  Fix
   by setting i2c_imx->slave = NULL on the error path.

2. In i2c_imx_unreg_slave(), the slave pointer is set to NULL after
   disabling interrupts.  However, a pending interrupt might already
   have started the hrtimer (i2c_imx_slave_timeout) before the pointer
   was cleared.  If the hrtimer fires after i2c_imx->slave is set to
   NULL, the timer callback i2c_imx_slave_finish_op() will call
   i2c_imx_slave_event() with a NULL slave pointer, and the
   last_slave_event check loop in i2c_imx_slave_finish_op() may cause
   a system hang because last_slave_event is no longer updated.  Fix
   by canceling the hrtimer and waiting for it to complete after
   disabling interrupts, before clearing the slave pointer.

Both issues can trigger a kernel oops, system hang, or permanent
slave registration failure under certain race conditions.  Add the
missing NULL assignment and the missing hrtimer cleanup to harden
the slave path.

Fixes: f7414cd6923f ("i2c: imx: support slave mode for imx I2C driver")
Cc: stable@vger.kernel.org
Signed-off-by: Liem <liem16213@gmail.com>
---
v1 -> v2:
  - Instead of adding a NULL check in i2c_imx_slave_event(), cancel
    the hrtimer and wait for it to finish in i2c_imx_unreg_slave()
    after disabling interrupts, as suggested by <Carlos Song>.
    This avoids a potential hang in the last_slave_event loop in
    i2c_imx_slave_finish_op().
---
 drivers/i2c/busses/i2c-imx.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index 28313d0fad37..04ffb927aba9 100644
--- a/drivers/i2c/busses/i2c-imx.c
+++ b/drivers/i2c/busses/i2c-imx.c
@@ -936,6 +936,7 @@ static int i2c_imx_reg_slave(struct i2c_client *client)
 	/* Resume */
 	ret = pm_runtime_resume_and_get(i2c_imx->adapter.dev.parent);
 	if (ret < 0) {
+		i2c_imx->slave = NULL;
 		dev_err(&i2c_imx->adapter.dev, "failed to resume i2c controller");
 		return ret;
 	}
@@ -957,7 +958,7 @@ static int i2c_imx_unreg_slave(struct i2c_client *client)
 	imx_i2c_write_reg(0, i2c_imx, IMX_I2C_IADR);
 
 	i2c_imx_reset_regs(i2c_imx);
-
+	hrtimer_cancel(&i2c_imx->slave_timer);
 	i2c_imx->slave = NULL;
 
 	/* Suspend */
-- 
2.53.0