[RFC kvm-unit-tests 24/27] arm: realm: Add helpers to decode RSI return codes

[Joey Gouly]

From: Suzuki K Poulose <suzuki.poulose@xxxxxxx>

RMM encodes error code and index in the result of an operation.
Add helpers to decode this information for use with the attestation
tests.

Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Signed-off-by: Joey Gouly <joey.gouly@xxxxxxx>
---
 lib/arm64/asm/rsi.h | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/lib/arm64/asm/rsi.h b/lib/arm64/asm/rsi.h
index 50bab993..1d01a929 100644
--- a/lib/arm64/asm/rsi.h
+++ b/lib/arm64/asm/rsi.h
@@ -16,6 +16,39 @@
 
 extern bool rsi_present;
 
+/*
+ * Logical representation of return code returned by RMM commands.
+ * Each failure mode of a given command should return a unique return code, so
+ * that the caller can use it to unambiguously identify the failure mode.  To
+ * avoid having a very large list of enumerated values, the return code is
+ * composed of a status which identifies the category of the error (for example,
+ * an address was misaligned), and an index which disambiguates between multiple
+ * similar failure modes (for example, a command may take multiple addresses as
+ * its input; the index identifies _which_ of them was misaligned.)
+ */
+typedef unsigned int status_t;
+typedef struct {
+	status_t status;
+	unsigned int index;
+} return_code_t;
+
+/*
+ * Convenience function for creating a return_code_t.
+ */
+static inline return_code_t make_return_code(unsigned int status,
+					     unsigned int index)
+{
+	return (return_code_t) {status, index};
+}
+
+/*
+ * Unpacks a return code.
+ */
+static inline return_code_t unpack_return_code(unsigned long error_code)
+{
+	return make_return_code(error_code & 0xff, error_code >> 8);
+}
+
 void arm_rsi_init(void);
 
 int rsi_invoke(unsigned int function_id, unsigned long arg0,
-- 
2.17.1