Hi heikki,

-----Original Message-----
From: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Sent: Monday, October 11, 2021 2:31 PM
To: Xu Yang <xu.yang_2@nxp.com>; linux@roeck-us.net
Cc: Jun Li <redacted>; gregkh@linuxfoundation.org; linux-
usb@vger.kernel.org; dl-linux-imx [off-list ref]
Subject: [EXT] Re: [PATCH v2] usb: typec: tcpm: fix issue of multiple
tcpm_set_state

Caution: EXT Email

Guenter, can you check this?

On Fri, Aug 27, 2021 at 07:48:09PM +0800, Xu Yang wrote:

quoted

There are potential problems when states are set as following:

    tcpm_set_state(A, 0)
    tcpm_set_state(B, X)

As long as the state A is set and the state_machine work is queued
successfully, state_machine work will be scheduled soon after. Before
running into tcpm_state_machine_work(), there is a chance to set state
B again. If it does occur:

either (X = 0)
    port->state = B and state_machine work is queued again, then work
    will be executed twice.
or (X != 0)
    port->state = A and port->delayed_state = B, then work will be
    executed once but timer is still running.

For this situation, tcpm should only handle the most recent state
change as if only one state is set just now. Therefore, if the
state_machine work has already been queued, it can't be queued again
before running into tcpm_state_machine_work().

The state_machine_running flag already prevents from queuing the work,
so we can make it contain the pending stage (after work be queued and
before running into tcpm_state_machine_work). The
state_machine_pending_or_running flag can be used to indicate that a
state can be handled without queuing the work again.

Because the state_machine work has been queued for state A, there is
no way to cancel as it may be already dequeued later, and then will
run into
tcpm_state_machine_work() certainly. To handle the delayed state B,
such an abnormal work should be skiped. If port->delayed_state !=
INVALID_STATE and timer is still running, it's time to skip.

Fixes: 4b4e02c83167 ("typec: tcpm: Move out of staging")
cc: <redacted>
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>

What changed since v1?

thanks,

In patch v1, I committed two patches to fix two problems. However, the two 
problems are resulted by the same reason. And I try to address the issues 
after it occurs.

In patch v2, according to Guenter's advice, I try to avoid such problems 
occurring from the source. So I set a state_machine_pending_or_running flag 
to indicate that a state can be handled without queuing the work again. 
Meanwhile, one patch is enough to address the problems.

Xu Yang

quoted

diff --git a/drivers/usb/typec/tcpm/tcpm.c

b/drivers/usb/typec/tcpm/tcpm.c index 049f4c61ee82..a913bc620e88
100644

--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c

@@ -371,7 +371,7 @@ struct tcpm_port {
      struct kthread_work enable_frs;
      struct hrtimer send_discover_timer;
      struct kthread_work send_discover_work;
-     bool state_machine_running;
+     bool state_machine_pending_or_running;
      bool vdm_sm_running;

      struct completion tx_complete;

@@ -1192,6 +1192,7 @@ static void mod_tcpm_delayed_work(struct

tcpm_port *port, unsigned int delay_ms)

quoted

      } else {
              hrtimer_cancel(&port->state_machine_timer);
              kthread_queue_work(port->wq, &port->state_machine);
+             port->state_machine_pending_or_running = true;
      }
 }

@@ -1250,7 +1251,7 @@ static void tcpm_set_state(struct tcpm_port

*port, enum tcpm_state state,

quoted

               * tcpm_state_machine_work() will continue running the state
               * machine.
               */
-             if (!port->state_machine_running)
+             if (!port->state_machine_pending_or_running)
                      mod_tcpm_delayed_work(port, 0);
      }
 }

@@ -4810,13 +4811,15 @@ static void tcpm_state_machine_work(struct

kthread_work *work)

quoted

      enum tcpm_state prev_state;

      mutex_lock(&port->lock);
-     port->state_machine_running = true;

      if (port->queued_message && tcpm_send_queued_message(port))
              goto done;

      /* If we were queued due to a delayed state change, update it now */
      if (port->delayed_state) {
+             if (ktime_before(ktime_get(), port->delayed_runtime))
+                     goto done;
+
              tcpm_log(port, "state change %s -> %s [delayed %ld ms]",
                       tcpm_states[port->state],
                       tcpm_states[port->delayed_state],
port->delay_ms); @@ -4837,7 +4840,7 @@ static void

tcpm_state_machine_work(struct kthread_work *work)

quoted

      } while (port->state != prev_state && !port->delayed_state);

 done:
-     port->state_machine_running = false;
+     port->state_machine_pending_or_running = false;
      mutex_unlock(&port->lock);
 }

@@ -6300,6 +6303,7 @@ static enum hrtimer_restart

state_machine_timer_handler(struct hrtimer *timer)

quoted

      struct tcpm_port *port = container_of(timer, struct tcpm_port,
state_machine_timer);

      kthread_queue_work(port->wq, &port->state_machine);
+     port->state_machine_pending_or_running = true;
      return HRTIMER_NORESTART;
 }

--
2.25.1

--
heikki