[PATCH] usb: typec: ucsi: Move unregister out of atomic section

[Bjorn Andersson <quic_bjorande@xxxxxxxxxxx>]

Commit '9329933699b3 ("soc: qcom: pmic_glink: Make client-lock
non-sleeping")' moved the pmic_glink client list under a spinlock, as it
is accessed by the rpmsg/glink callback, which in turn is invoked from
IRQ context.

This means that ucsi_unregister() is now called from atomic context,
which isn't feasible as it's expecting a sleepable context. An effort is
under way to get GLINK to invoke its callbacks in a sleepable context,
but until then lets schedule the unregistration.

A side effect of this is that ucsi_unregister() can now happen
after the remote processor, and thereby the communication link with it, is
gone. pmic_glink_send() is amended with a check to avoid the resulting NULL
pointer dereference.
This does however result in the user being informed about this error by
the following entry in the kernel log:

  ucsi_glink.pmic_glink_ucsi pmic_glink.ucsi.0: failed to send UCSI write request: -5

Fixes: 9329933699b3 ("soc: qcom: pmic_glink: Make client-lock non-sleeping")
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
Reviewed-by: Neil Armstrong <neil.armstrong@xxxxxxxxxx>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
Tested-by: Amit Pundir <amit.pundir@xxxxxxxxxx>
Reviewed-by: Johan Hovold <johan+linaro@xxxxxxxxxx>
Tested-by: Johan Hovold <johan+linaro@xxxxxxxxxx>
Signed-off-by: Bjorn Andersson <quic_bjorande@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20240820-pmic-glink-v6-11-races-v3-2-eec53c750a04@xxxxxxxxxxx
Signed-off-by: Bjorn Andersson <andersson@xxxxxxxxxx>

diff --git a/drivers/soc/qcom/pmic_glink.c b/drivers/soc/qcom/pmic_glink.c
index 53b176d04fbd..b218460219b7 100644
--- a/drivers/soc/qcom/pmic_glink.c
+++ b/drivers/soc/qcom/pmic_glink.c
@@ -112,8 +112,16 @@ EXPORT_SYMBOL_GPL(pmic_glink_client_register);
 int pmic_glink_send(struct pmic_glink_client *client, void *data, size_t len)
 {
 	struct pmic_glink *pg = client->pg;
+	int ret;
 
-	return rpmsg_send(pg->ept, data, len);
+	mutex_lock(&pg->state_lock);
+	if (!pg->ept)
+		ret = -ECONNRESET;
+	else
+		ret = rpmsg_send(pg->ept, data, len);
+	mutex_unlock(&pg->state_lock);
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(pmic_glink_send);
 
diff --git a/drivers/usb/typec/ucsi/ucsi_glink.c b/drivers/usb/typec/ucsi/ucsi_glink.c
index f6f4fae40399..6aace19d595b 100644
--- a/drivers/usb/typec/ucsi/ucsi_glink.c
+++ b/drivers/usb/typec/ucsi/ucsi_glink.c
@@ -68,6 +68,9 @@ struct pmic_glink_ucsi {
 
 	struct work_struct notify_work;
 	struct work_struct register_work;
+	spinlock_t state_lock;
+	bool ucsi_registered;
+	bool pd_running;
 
 	u8 read_buf[UCSI_BUF_SIZE];
 };
@@ -244,8 +247,20 @@ static void pmic_glink_ucsi_notify(struct work_struct *work)
 static void pmic_glink_ucsi_register(struct work_struct *work)
 {
 	struct pmic_glink_ucsi *ucsi = container_of(work, struct pmic_glink_ucsi, register_work);
+	unsigned long flags;
+	bool pd_running;
 
-	ucsi_register(ucsi->ucsi);
+	spin_lock_irqsave(&ucsi->state_lock, flags);
+	pd_running = ucsi->pd_running;
+	spin_unlock_irqrestore(&ucsi->state_lock, flags);
+
+	if (!ucsi->ucsi_registered && pd_running) {
+		ucsi_register(ucsi->ucsi);
+		ucsi->ucsi_registered = true;
+	} else if (ucsi->ucsi_registered && !pd_running) {
+		ucsi_unregister(ucsi->ucsi);
+		ucsi->ucsi_registered = false;
+	}
 }
 
 static void pmic_glink_ucsi_callback(const void *data, size_t len, void *priv)
@@ -269,11 +284,12 @@ static void pmic_glink_ucsi_callback(const void *data, size_t len, void *priv)
 static void pmic_glink_ucsi_pdr_notify(void *priv, int state)
 {
 	struct pmic_glink_ucsi *ucsi = priv;
+	unsigned long flags;
 
-	if (state == SERVREG_SERVICE_STATE_UP)
-		schedule_work(&ucsi->register_work);
-	else if (state == SERVREG_SERVICE_STATE_DOWN)
-		ucsi_unregister(ucsi->ucsi);
+	spin_lock_irqsave(&ucsi->state_lock, flags);
+	ucsi->pd_running = (state == SERVREG_SERVICE_STATE_UP);
+	spin_unlock_irqrestore(&ucsi->state_lock, flags);
+	schedule_work(&ucsi->register_work);
 }
 
 static void pmic_glink_ucsi_destroy(void *data)
@@ -320,6 +336,7 @@ static int pmic_glink_ucsi_probe(struct auxiliary_device *adev,
 	INIT_WORK(&ucsi->register_work, pmic_glink_ucsi_register);
 	init_completion(&ucsi->read_ack);
 	init_completion(&ucsi->write_ack);
+	spin_lock_init(&ucsi->state_lock);
 	mutex_init(&ucsi->lock);
 
 	ucsi->ucsi = ucsi_create(dev, &pmic_glink_ucsi_ops);