Commit 67c3f99b authored by Cosmin Tanislav's avatar Cosmin Tanislav Committed by William Breathitt Gray
Browse files

counter: rz-mtu3-cnt: prevent counter from being toggled multiple times 



Runtime PM counter is incremented / decremented each time the sysfs
enable file is written to.

If user writes 0 to the sysfs enable file multiple times, runtime PM
usage count underflows, generating the following message.

rz-mtu3-counter rz-mtu3-counter.0: Runtime PM usage count underflow!

At the same time, hardware registers end up being accessed with clocks
off in rz_mtu3_terminate_counter() to disable an already disabled
channel.

If user writes 1 to the sysfs enable file multiple times, runtime PM
usage count will be incremented each time, requiring the same number of
0 writes to get it back to 0.

If user writes 0 to the sysfs enable file while PWM is in progress, PWM
is stopped without counter being the owner of the underlying MTU3
channel.

Check against the cached count_is_enabled value and exit if the user
is trying to set the same enable value.

Cc: stable@vger.kernel.org
Fixes: 0be89073 ("counter: Add Renesas RZ/G2L MTU3a counter driver")
Signed-off-by: default avatarCosmin Tanislav <cosmin-gabriel.tanislav.xa@renesas.com>
Link: https://lore.kernel.org/r/20260130122353.2263273-5-cosmin-gabriel.tanislav.xa@renesas.com


Signed-off-by: default avatarWilliam Breathitt Gray <wbg@kernel.org>
parent f338e773

drivers/counter/rz-mtu3-cnt.c

+8 −4
Original line number Diff line number Diff line
@@ -499,21 +499,25 @@ static int rz_mtu3_count_enable_write(struct counter_device *counter, 
	struct rz_mtu3_cnt *const priv = counter_priv(counter);

	int ret = 0;



	if (enable) {

	mutex_lock(&priv->lock);



	if (priv->count_is_enabled[count->id] == enable)

		goto exit;



	if (enable) {

		pm_runtime_get_sync(ch->dev);

		ret = rz_mtu3_initialize_counter(counter, count->id);

		if (ret == 0)

			priv->count_is_enabled[count->id] = true;

		mutex_unlock(&priv->lock);

	} else {

		mutex_lock(&priv->lock);

		rz_mtu3_terminate_counter(counter, count->id);

		priv->count_is_enabled[count->id] = false;

		pm_runtime_put(ch->dev);

		mutex_unlock(&priv->lock);

	}



exit:

	mutex_unlock(&priv->lock);



	return ret;

}