If ACPI advertises an FF-A based TPM but the tpm_crb_ffa driver is not
enabled via Kconfig, inline stub versions of the interface functions
are used. These functions incorrectly return 0, which indicates success.
The result is that the tpm_crb probe function continues execution and
eventually detects a timeout at the TPM.

Change the inline functions to return errors, so that probe() sees that
tpm_crb_ffa is not present and aborts the probe.

Signed-off-by: Stuart Yoder <stuart.yoder@arm.com>
---
 drivers/char/tpm/tpm_crb_ffa.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/char/tpm/tpm_crb_ffa.h b/drivers/char/tpm/tpm_crb_ffa.h
index 645c41ede10ed..c006403e2f14b 100644
--- a/drivers/char/tpm/tpm_crb_ffa.h
+++ b/drivers/char/tpm/tpm_crb_ffa.h
@@ -14,9 +14,9 @@ int tpm_crb_ffa_init(void);
 int tpm_crb_ffa_get_interface_version(u16 *major, u16 *minor);
 int tpm_crb_ffa_start(int request_type, int locality);
 #else
-static inline int tpm_crb_ffa_init(void) { return 0; }
-static inline int tpm_crb_ffa_get_interface_version(u16 *major, u16 *minor) { return 0; }
-static inline int tpm_crb_ffa_start(int request_type, int locality) { return 0; }
+static inline int tpm_crb_ffa_init(void) { return -ENODEV; }
+static inline int tpm_crb_ffa_get_interface_version(u16 *major, u16 *minor) { return -ENODEV; }
+static inline int tpm_crb_ffa_start(int request_type, int locality) { return -ENODEV; }
 #endif
 
 #define CRB_FFA_START_TYPE_COMMAND 0
-- 
2.34.1

On Mon, Apr 14, 2025 at 09:52:35AM -0500, Stuart Yoder wrote:
> If ACPI advertises an FF-A based TPM but the tpm_crb_ffa driver is not
> enabled via Kconfig, inline stub versions of the interface functions
> are used. These functions incorrectly return 0, which indicates success.
> The result is that the tpm_crb probe function continues execution and
> eventually detects a timeout at the TPM.
> 
> Change the inline functions to return errors, so that probe() sees that
> tpm_crb_ffa is not present and aborts the probe.
> 

LGTM,

Acked-by: Sudeep Holla <sudeep.holla@arm.com>

-- 
Regards,
Sudeep