target/arm: Implement M-profile "minimal RAS implementation"

For v8.1M the architecture mandates that CPUs must provide at
least the "minimal RAS implementation" from the Reliability,
Availability and Serviceability extension. This consists of:
 * an ESB instruction which is a NOP
   -- since it is in the HINT space we need only add a comment
 * an RFSR register which will RAZ/WI
 * a RAZ/WI AIRCR.IESB bit
   -- the code which handles writes to AIRCR does not allow setting
      of RES0 bits, so we already treat this as RAZ/WI; add a comment
      noting that this is deliberate
 * minimal implementation of the RAS register block at 0xe0005000
   -- this will be in a subsequent commit
 * setting the ID_PFR0.RAS field to 0b0010
   -- we will do this when we add the Cortex-M55 CPU model

Signed-off-by: Peter Maydell <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Message-id: [email protected]

hw/intc/armv7m_nvic.c

@@ -1483,6 +1483,12 @@ static uint32_t nvic_readl(NVICState *s, uint32_t offset, MemTxAttrs attrs)
             return 0;
         }
         return cpu->env.v7m.sfar;
+    case 0xf04: /* RFSR */
+        if (!cpu_isar_feature(aa32_ras, cpu)) {
+            goto bad_offset;
+        }
+        /* We provide minimal-RAS only: RFSR is RAZ/WI */
+        return 0;
     case 0xf34: /* FPCCR */
         if (!cpu_isar_feature(aa32_vfp_simd, cpu)) {
             return 0;
@@ -1611,6 +1617,7 @@ static void nvic_writel(NVICState *s, uint32_t offset, uint32_t value,
                               R_V7M_AIRCR_PRIGROUP_SHIFT,
                               R_V7M_AIRCR_PRIGROUP_LENGTH);
             }
+            /* AIRCR.IESB is RAZ/WI because we implement only minimal RAS */
             if (attrs.secure) {
                 /* These bits are only writable by secure */
                 cpu->env.v7m.aircr = value &
@@ -2026,6 +2033,12 @@ static void nvic_writel(NVICState *s, uint32_t offset, uint32_t value,
         }
         break;
     }
+    case 0xf04: /* RFSR */
+        if (!cpu_isar_feature(aa32_ras, cpu)) {
+            goto bad_offset;
+        }
+        /* We provide minimal-RAS only: RFSR is RAZ/WI */
+        break;
     case 0xf34: /* FPCCR */
         if (cpu_isar_feature(aa32_vfp_simd, cpu)) {
             /* Not all bits here are banked. */

target/arm/cpu.h

@@ -1827,6 +1827,15 @@ FIELD(ID_MMFR4, LSM, 20, 4)
 FIELD(ID_MMFR4, CCIDX, 24, 4)
 FIELD(ID_MMFR4, EVT, 28, 4)
 
+FIELD(ID_PFR0, STATE0, 0, 4)
+FIELD(ID_PFR0, STATE1, 4, 4)
+FIELD(ID_PFR0, STATE2, 8, 4)
+FIELD(ID_PFR0, STATE3, 12, 4)
+FIELD(ID_PFR0, CSV2, 16, 4)
+FIELD(ID_PFR0, AMU, 20, 4)
+FIELD(ID_PFR0, DIT, 24, 4)
+FIELD(ID_PFR0, RAS, 28, 4)
+
 FIELD(ID_PFR1, PROGMOD, 0, 4)
 FIELD(ID_PFR1, SECURITY, 4, 4)
 FIELD(ID_PFR1, MPROGMOD, 8, 4)
@@ -3573,6 +3582,11 @@ static inline bool isar_feature_aa32_predinv(const ARMISARegisters *id)
     return FIELD_EX32(id->id_isar6, ID_ISAR6, SPECRES) != 0;
 }
 
+static inline bool isar_feature_aa32_ras(const ARMISARegisters *id)
+{
+    return FIELD_EX32(id->id_pfr0, ID_PFR0, RAS) != 0;
+}
+
 static inline bool isar_feature_aa32_mprofile(const ARMISARegisters *id)
 {
     return FIELD_EX32(id->id_pfr1, ID_PFR1, MPROGMOD) != 0;

target/arm/t32.decode

@@ -307,6 +307,10 @@ CLZ              1111 1010 1011 ---- 1111 .... 1000 ....      @rdm
       # SEV      1111 0011 1010 1111 1000 0000 0000 0100
       # SEVL     1111 0011 1010 1111 1000 0000 0000 0101
 
+      # For M-profile minimal-RAS ESB can be a NOP, which is the
+      # default behaviour since it is in the hint space.
+      # ESB      1111 0011 1010 1111 1000 0000 0001 0000
+
       # The canonical nop ends in 0000 0000, but the whole rest
       # of the space is "reserved hint, behaves as nop".
       NOP        1111 0011 1010 1111 1000 0000 ---- ----