firmware: arm_ffa: Explicitly cast return value from NOTIFICATION_INFO_GET

The return value ret.a2 is of type unsigned long and FFA_RET_NO_DATA is
a negative value.

Since the return value from the firmware can be just 32-bit even on
64-bit systems as FFA specification mentions it as int32 error code in
w0 register, explicitly casting to s32 ensures correct sign interpretation
when comparing against a signed error code FFA_RET_NO_DATA.

Without casting, comparison between unsigned long and a negative
constant could lead to unintended results due to type promotions.

Fixes: 3522be4 ("firmware: arm_ffa: Implement the NOTIFICATION_INFO_GET interface")
Reported-by: Andrei Homescu <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Sudeep Holla <[email protected]>

Author: sudeep-holla

drivers/firmware/arm_ffa/driver.c

@@ -976,7 +976,7 @@ static void ffa_notification_info_get(void)
 			  }, &ret);
 
 		if (ret.a0 != FFA_FN_NATIVE(SUCCESS) && ret.a0 != FFA_SUCCESS) {
-			if (ret.a2 != FFA_RET_NO_DATA)
+			if ((s32)ret.a2 != FFA_RET_NO_DATA)
 				pr_err("Notification Info fetch failed: 0x%lx (0x%lx)",
 				       ret.a0, ret.a2);
 			return;