powerpc/pseries: Add helper to get PLPKS password length

Add helper function to get the PLPKS password length. This will be used
in a later patch to support passing the password between kernels over
kexec.

Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230210080401.345462-23-ajd@linux.ibm.com

arch/powerpc/include/asm/plpks.h

@@ -171,6 +171,11 @@ u32 plpks_get_maxlargeobjectsize(void);
  */
 u64 plpks_get_signedupdatealgorithms(void);
 
+/**
+ * Returns the length of the PLPKS password in bytes.
+ */
+u16 plpks_get_passwordlen(void);
+
 #endif // CONFIG_PSERIES_PLPKS
 
 #endif // _ASM_POWERPC_PLPKS_H

arch/powerpc/platforms/pseries/plpks.c

@@ -359,6 +359,11 @@ u64 plpks_get_signedupdatealgorithms(void)
 	return signedupdatealgorithms;
 }
 
+u16 plpks_get_passwordlen(void)
+{
+	return ospasswordlength;
+}
+
 bool plpks_is_available(void)
 {
 	int rc;