[PATCH 2/2] scsi: ufs: rpmb: Register and unregister ufs_rpmb_bus_type

[Stanley Jhu <stanleyjhu@google.com>]

The UFS RPMB driver assigns its devices to a custom ufs_rpmb_bus_type,
but never registers this bus with the driver core. As a result,
device_register() fails during probe because the driver core rejects
devices attached to unregistered buses with -EINVAL:
  "bus_add_device: cannot add device 'ufs_rpmb0' to unregistered bus
   'ufs_rpmb'"
  "ufshcd: Failed to register UFS RPMB device 0"

Resolve this by integrating the bus into the UFS core lifecycle:

1. Bus registration and lifecycle:
   Register ufs_rpmb_bus_type during ufshcd_core_init() before any
   device probe occurs, and unregister it during ufshcd_core_exit().
   Annotate the registration helper with __init to allow init memory
   reclamation.

2. Modular reachability:
   Guard bus helper prototypes with IS_REACHABLE(CONFIG_RPMB) and provide
   inline stubs, preventing link failures when UFS is built-in and RPMB
   is compiled as a module.

Fixes: b06b8c421485 ("scsi: ufs: core: Add OP-TEE based RPMB driver for UFS devices")
Signed-off-by: Stanley Jhu <stanleyjhu@google.com>
---
 drivers/ufs/core/ufs-rpmb.c    | 10 ++++++++++
 drivers/ufs/core/ufshcd-priv.h | 11 ++++++++++-
 drivers/ufs/core/ufshcd.c      | 16 ++++++++++++++--
 3 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/drivers/ufs/core/ufs-rpmb.c b/drivers/ufs/core/ufs-rpmb.c
index 4f41d0b64d20..cf8982824b14 100644
--- a/drivers/ufs/core/ufs-rpmb.c
+++ b/drivers/ufs/core/ufs-rpmb.c
@@ -29,6 +29,16 @@ static const struct bus_type ufs_rpmb_bus_type = {
 	.name = "ufs_rpmb",
 };
 
+int __init ufs_rpmb_bus_register(void)
+{
+	return bus_register(&ufs_rpmb_bus_type);
+}
+
+void ufs_rpmb_bus_unregister(void)
+{
+	bus_unregister(&ufs_rpmb_bus_type);
+}
+
 /* UFS RPMB device structure */
 struct ufs_rpmb_dev {
 	u8 region_id;
diff --git a/drivers/ufs/core/ufshcd-priv.h b/drivers/ufs/core/ufshcd-priv.h
index e55c2a02c1f5..415f9230b164 100644
--- a/drivers/ufs/core/ufshcd-priv.h
+++ b/drivers/ufs/core/ufshcd-priv.h
@@ -493,10 +493,19 @@ static inline u32 ufshcd_mcq_get_sq_head_slot(struct ufs_hw_queue *q)
 	return val / sizeof(struct utp_transfer_req_desc);
 }
 
-#if IS_ENABLED(CONFIG_RPMB)
+#if IS_REACHABLE(CONFIG_RPMB)
+int __init ufs_rpmb_bus_register(void);
+void ufs_rpmb_bus_unregister(void);
 int ufs_rpmb_probe(struct ufs_hba *hba);
 void ufs_rpmb_remove(struct ufs_hba *hba);
 #else
+static inline int ufs_rpmb_bus_register(void)
+{
+	return 0;
+}
+static inline void ufs_rpmb_bus_unregister(void)
+{
+}
 static inline int ufs_rpmb_probe(struct ufs_hba *hba)
 {
 	return 0;
diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index a25b6a0cb5c6..4470e3d65c5c 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -11584,16 +11584,28 @@ static int __init ufshcd_core_init(void)
 
 	ufs_debugfs_init();
 
+	ret = ufs_rpmb_bus_register();
+	if (ret)
+		goto err_debugfs;
+
 	ret = scsi_register_driver(&ufs_dev_wlun_template);
 	if (ret)
-		ufs_debugfs_exit();
+		goto err_rpmb_bus;
+
+	return 0;
+
+err_rpmb_bus:
+	ufs_rpmb_bus_unregister();
+err_debugfs:
+	ufs_debugfs_exit();
 	return ret;
 }
 
 static void __exit ufshcd_core_exit(void)
 {
-	ufs_debugfs_exit();
 	scsi_unregister_driver(&ufs_dev_wlun_template);
+	ufs_rpmb_bus_unregister();
+	ufs_debugfs_exit();
 }
 
 module_init(ufshcd_core_init);
-- 
2.55.0.979.g7e5102b832-goog