soc: qcom: pmic_glink: Fix race during initialization

As pointed out by Stephen Boyd it is possible that during initialization
of the pmic_glink child drivers, the protection-domain notifiers fires,
and the associated work is scheduled, before the client registration
returns and as a result the local "client" pointer has been initialized.

The outcome of this is a NULL pointer dereference as the "client"
pointer is blindly dereferenced.

Timeline provided by Stephen:
CPU0 CPU1
---- ----
ucsi->client = NULL;
devm_pmic_glink_register_client()
client->pdr_notify(client->priv, pg->client_state)
pmic_glink_ucsi_pdr_notify()
schedule_work(&ucsi->register_work)
<schedule away>
pmic_glink_ucsi_register()
ucsi_register()
pmic_glink_ucsi_read_version()
pmic_glink_ucsi_read()
pmic_glink_ucsi_read()
pmic_glink_send(ucsi->client)
<client is NULL BAD>
ucsi->client = client // Too late!

This code is identical across the altmode, battery manager and usci
child drivers.

Resolve this by splitting the allocation of the "client" object and the
registration thereof into two operations.

This only happens if the protection domain registry is populated at the
time of registration, which by the introduction of commit '1ebcde047c54
("soc: qcom: add pd-mapper implementation")' became much more likely.

Reported-by: Amit Pundir <[e-mail]>
Closes: https://lore.kernel.org/all/[e-mail]/
Reported-by: Johan Hovold <[e-mail]>
Closes: https://lore.kernel.org/all/[e-mail]/
Reported-by: Stephen Boyd <[e-mail]>
Closes: https://lore.kernel.org/all/[e-mail]/
Fixes: 58ef4ece1e41 ("soc: qcom: pmic_glink: Introduce base PMIC GLINK driver")
Cc: [e-mail]
Reviewed-by: Heikki Krogerus <[e-mail]>
Reviewed-by: Neil Armstrong <[e-mail]>
Tested-by: Amit Pundir <[e-mail]>
Reviewed-by: Johan Hovold <[e-mail]>
Acked-by: Sebastian Reichel <[e-mail]>
Tested-by: Johan Hovold <[e-mail]>
Signed-off-by: Bjorn Andersson <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Bjorn Andersson <[e-mail]>

drivers/power/supply/qcom_battmgr.c

···
 					     "failed to register wireless charing power supply\n");
 	}
 
-	battmgr->client = devm_pmic_glink_register_client(dev,
-							  PMIC_GLINK_OWNER_BATTMGR,
-							  qcom_battmgr_callback,
-							  qcom_battmgr_pdr_notify,
-							  battmgr);
-	return PTR_ERR_OR_ZERO(battmgr->client);
+	battmgr->client = devm_pmic_glink_client_alloc(dev, PMIC_GLINK_OWNER_BATTMGR,
+						       qcom_battmgr_callback,
+						       qcom_battmgr_pdr_notify,
+						       battmgr);
+	if (IS_ERR(battmgr->client))
+		return PTR_ERR(battmgr->client);
+
+	pmic_glink_client_register(battmgr->client);
+
+	return 0;
 }
 
 static const struct auxiliary_device_id qcom_battmgr_id_table[] = {

drivers/soc/qcom/pmic_glink.c

···
 	spin_unlock_irqrestore(&pg->client_lock, flags);
 }
 
-struct pmic_glink_client *devm_pmic_glink_register_client(struct device *dev,
-							  unsigned int id,
-							  void (*cb)(const void *, size_t, void *),
-							  void (*pdr)(void *, int),
-							  void *priv)
+struct pmic_glink_client *devm_pmic_glink_client_alloc(struct device *dev,
+						       unsigned int id,
+						       void (*cb)(const void *, size_t, void *),
+						       void (*pdr)(void *, int),
+						       void *priv)
 {
 	struct pmic_glink_client *client;
 	struct pmic_glink *pg = dev_get_drvdata(dev->parent);
-	unsigned long flags;
 
 	client = devres_alloc(_devm_pmic_glink_release_client, sizeof(*client), GFP_KERNEL);
 	if (!client)
···
 	client->cb = cb;
 	client->pdr_notify = pdr;
 	client->priv = priv;
+	INIT_LIST_HEAD(&client->node);
+
+	devres_add(dev, client);
+
+	return client;
+}
+EXPORT_SYMBOL_GPL(devm_pmic_glink_client_alloc);
+
+void pmic_glink_client_register(struct pmic_glink_client *client)
+{
+	struct pmic_glink *pg = client->pg;
+	unsigned long flags;
 
 	mutex_lock(&pg->state_lock);
 	spin_lock_irqsave(&pg->client_lock, flags);
···
 	spin_unlock_irqrestore(&pg->client_lock, flags);
 	mutex_unlock(&pg->state_lock);
 
-	devres_add(dev, client);
-
-	return client;
 }
-EXPORT_SYMBOL_GPL(devm_pmic_glink_register_client);
+EXPORT_SYMBOL_GPL(pmic_glink_client_register);
 
 int pmic_glink_send(struct pmic_glink_client *client, void *data, size_t len)
 {

drivers/soc/qcom/pmic_glink_altmode.c

···
 			return ret;
 	}
 
-	altmode->client = devm_pmic_glink_register_client(dev,
-							  altmode->owner_id,
-							  pmic_glink_altmode_callback,
-							  pmic_glink_altmode_pdr_notify,
-							  altmode);
-	return PTR_ERR_OR_ZERO(altmode->client);
+	altmode->client = devm_pmic_glink_client_alloc(dev,
+						       altmode->owner_id,
+						       pmic_glink_altmode_callback,
+						       pmic_glink_altmode_pdr_notify,
+						       altmode);
+	if (IS_ERR(altmode->client))
+		return PTR_ERR(altmode->client);
+
+	pmic_glink_client_register(altmode->client);
+
+	return 0;
 }
 
 static const struct auxiliary_device_id pmic_glink_altmode_id_table[] = {

drivers/usb/typec/ucsi/ucsi_glink.c

···
 		ucsi->port_orientation[port] = desc;
 	}
 
-	ucsi->client = devm_pmic_glink_register_client(dev,
-						       PMIC_GLINK_OWNER_USBC,
-						       pmic_glink_ucsi_callback,
-						       pmic_glink_ucsi_pdr_notify,
-						       ucsi);
-	return PTR_ERR_OR_ZERO(ucsi->client);
+	ucsi->client = devm_pmic_glink_client_alloc(dev, PMIC_GLINK_OWNER_USBC,
+						    pmic_glink_ucsi_callback,
+						    pmic_glink_ucsi_pdr_notify,
+						    ucsi);
+	if (IS_ERR(ucsi->client))
+		return PTR_ERR(ucsi->client);
+
+	pmic_glink_client_register(ucsi->client);
+
+	return 0;
 }
 
 static void pmic_glink_ucsi_remove(struct auxiliary_device *adev)

include/linux/soc/qcom/pmic_glink.h

···
 
 int pmic_glink_send(struct pmic_glink_client *client, void *data, size_t len);
 
-struct pmic_glink_client *devm_pmic_glink_register_client(struct device *dev,
-							  unsigned int id,
-							  void (*cb)(const void *, size_t, void *),
-							  void (*pdr)(void *, int),
-							  void *priv);
+struct pmic_glink_client *devm_pmic_glink_client_alloc(struct device *dev,
+						       unsigned int id,
+						       void (*cb)(const void *, size_t, void *),
+						       void (*pdr)(void *, int),
+						       void *priv);
+void pmic_glink_client_register(struct pmic_glink_client *client);
 
 #endif