tests: Add test for ASID2 and write/read of feature bits

Test for presence of ASID2; if it is, check FNG1, FNG0, and A2 are
writable, and read value shows the update. If not present, check these
read as RES0.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Jim MacArthur <jim.macarthur@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

tests/tcg/aarch64/system/asid2.c

@@ -0,0 +1,76 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ *
+ * ASID2 Feature presence and enabled TCR2_EL1 bits test
+ *
+ * Copyright (c) 2025 Linaro Ltd
+ *
+ */
+
+#include <stdint.h>
+#include <minilib.h>
+
+#define ID_AA64MMFR3_EL1 "S3_0_C0_C7_3"
+#define ID_AA64MMFR4_EL1 "S3_0_C0_C7_4"
+#define TCR2_EL1 "S3_0_C2_C0_3"
+
+int main()
+{
+    /*
+     * Test for presence of ASID2 and three feature bits enabled by it:
+     * https://developer.arm.com/documentation/109697/2025_09/Feature-descriptions/The-Armv9-5-architecture-extension
+     * Bits added are FNG1, FNG0, and A2. These should be RES0 if A2 is
+     * not enabled and read as the written value if A2 is enabled.
+     */
+
+    uint64_t out;
+    uint64_t idreg3;
+    uint64_t idreg4;
+    int tcr2_present;
+    int asid2_present;
+
+    /* Mask is FNG1, FNG0, and A2 */
+    const uint64_t feature_mask = (1ULL << 18 | 1ULL << 17 | 1ULL << 16);
+    const uint64_t in = feature_mask;
+
+    asm("mrs %[idreg3], " ID_AA64MMFR3_EL1 "\n\t"
+        : [idreg3] "=r" (idreg3));
+
+    tcr2_present = ((idreg3 & 0xF) != 0);
+
+    if (!tcr2_present) {
+        ml_printf("TCR2 is not present, cannot perform test");
+        return 0;
+    }
+
+    asm("mrs %[idreg4], " ID_AA64MMFR4_EL1 "\n\t"
+        : [idreg4] "=r" (idreg4));
+
+    asid2_present = ((idreg4 & 0xF00) != 0);
+
+    asm("msr " TCR2_EL1 ", %[x0]\n\t"
+        "mrs %[x1], " TCR2_EL1 "\n\t"
+        : [x1] "=r" (out)
+        : [x0] "r" (in));
+
+    if (asid2_present) {
+        if ((out & feature_mask) == in) {
+            ml_printf("OK\n");
+            return 0;
+        } else {
+            ml_printf("FAIL: ASID2 present, but read value %lx != "
+                      "written value %lx\n",
+                      out & feature_mask, in);
+            return 1;
+        }
+    } else {
+        if (out == 0) {
+            ml_printf("TCR2_EL1 reads as RES0 as expected\n");
+            return 0;
+        } else {
+            ml_printf("FAIL: ASID2, missing but read value %lx != 0\n",
+                      out & feature_mask, in);
+            return 1;
+        }
+    }
+}