target-arm: Implement MDCR_EL2.TDRA traps

Implement trapping of the "debug ROM" registers, which are controlled
by MDCR_EL2.TDRA for EL2 but by the more general MDCR_EL3.TDA for EL3.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NSergey Fedorov <serge.fdrv@gmail.com>

target-arm/helper.c

@@ -403,6 +403,24 @@ static CPAccessResult access_tdosa(CPUARMState *env, const ARMCPRegInfo *ri,
     return CP_ACCESS_OK;
 }
 
+/* Check for traps to "debug ROM" registers, which are controlled
+ * by MDCR_EL2.TDRA for EL2 but by the more general MDCR_EL3.TDA for EL3.
+ */
+static CPAccessResult access_tdra(CPUARMState *env, const ARMCPRegInfo *ri,
+                                  bool isread)
+{
+    int el = arm_current_el(env);
+
+    if (el < 2 && (env->cp15.mdcr_el2 & MDCR_TDRA)
+        && !arm_is_secure_below_el3(env)) {
+        return CP_ACCESS_TRAP_EL2;
+    }
+    if (el < 3 && (env->cp15.mdcr_el3 & MDCR_TDA)) {
+        return CP_ACCESS_TRAP_EL3;
+    }
+    return CP_ACCESS_OK;
+}
+
 static void dacr_write(CPUARMState *env, const ARMCPRegInfo *ri, uint64_t value)
 {
     ARMCPU *cpu = arm_env_get_cpu(env);
@@ -3773,12 +3791,15 @@ static const ARMCPRegInfo debug_cp_reginfo[] = {
      * accessor.
      */
     { .name = "DBGDRAR", .cp = 14, .crn = 1, .crm = 0, .opc1 = 0, .opc2 = 0,
-      .access = PL0_R, .type = ARM_CP_CONST, .resetvalue = 0 },
+      .access = PL0_R, .accessfn = access_tdra,
+      .type = ARM_CP_CONST, .resetvalue = 0 },
     { .name = "MDRAR_EL1", .state = ARM_CP_STATE_AA64,
       .opc0 = 2, .opc1 = 0, .crn = 1, .crm = 0, .opc2 = 0,
-      .access = PL1_R, .type = ARM_CP_CONST, .resetvalue = 0 },
+      .access = PL1_R, .accessfn = access_tdra,
+      .type = ARM_CP_CONST, .resetvalue = 0 },
     { .name = "DBGDSAR", .cp = 14, .crn = 2, .crm = 0, .opc1 = 0, .opc2 = 0,
-      .access = PL0_R, .type = ARM_CP_CONST, .resetvalue = 0 },
+      .access = PL0_R, .accessfn = access_tdra,
+      .type = ARM_CP_CONST, .resetvalue = 0 },
     /* Monitor debug system control register; the 32-bit alias is DBGDSCRext. */
     { .name = "MDSCR_EL1", .state = ARM_CP_STATE_BOTH,
       .cp = 14, .opc0 = 2, .opc1 = 0, .crn = 0, .crm = 2, .opc2 = 2,