[PATCH] scsi: ufs: core: Fix link error when CONFIG_RPMB=m

[Bean Huo <beanhuo@iokpp.de>]

From: Bean Huo <beanhuo@micron.com>

When CONFIG_SCSI_UFSHCD=y and CONFIG_RPMB=m, the kernel fails to link
with undefined references to ufs_rpmb_probe() and ufs_rpmb_remove():

  ld: drivers/ufs/core/ufshcd.c:8950: undefined reference to `ufs_rpmb_probe'
  ld: drivers/ufs/core/ufshcd.c:10505: undefined reference to `ufs_rpmb_remove'

The issue occurs because IS_ENABLED(CONFIG_RPMB) evaluates to true when
CONFIG_RPMB=m, causing the header to declare the real function prototypes.
However, the Makefile line:

  ufshcd-core-$(CONFIG_RPMB) += ufs-rpmb.o

only adds ufs-rpmb.o when CONFIG_RPMB=y (builtin), not when CONFIG_RPMB=m.
This results in the functions being called but not linked into the kernel.

Fix this by changing IS_ENABLED() to IS_BUILTIN(), ensuring the real
functions are only declared when ufs-rpmb.o is actually compiled into
ufshcd-core.

Fixes: b06b8c421485 ("scsi: ufs: core: Add OP-TEE based RPMB driver for UFS devices")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202511300443.h7sotuL0-lkp@intel.com/
Signed-off-by: Bean Huo <beanhuo@micron.com>
---
 drivers/ufs/core/ufshcd-priv.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/ufs/core/ufshcd-priv.h b/drivers/ufs/core/ufshcd-priv.h
index 4259f499382f..9bab6aada072 100644
--- a/drivers/ufs/core/ufshcd-priv.h
+++ b/drivers/ufs/core/ufshcd-priv.h
@@ -438,7 +438,7 @@ 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_BUILTIN(CONFIG_RPMB)
 int ufs_rpmb_probe(struct ufs_hba *hba);
 void ufs_rpmb_remove(struct ufs_hba *hba);
 #else
-- 
2.34.1