target-mips: add Config5.FRE support allowing Status.FR=0 emulation

This relatively small architectural feature adds the following:

FIR.FREP: Read-only. If FREP=1, then Config5.FRE and Config5.UFE are
          available.

Config5.FRE: When enabled all single-precision FP arithmetic instructions,
             LWC1/LWXC1/MTC1, SWC1/SWXC1/MFC1 cause a Reserved Instructions
             exception.

Config5.UFE: Allows user to write/read Config5.FRE using CTC1/CFC1
             instructions.

Enable the feature in MIPS64R6-generic CPU.
Signed-off-by: NLeon Alrae <leon.alrae@imgtec.com>

target-mips/cpu.h

@@ -100,6 +100,7 @@ struct CPUMIPSFPUContext {
     float_status fp_status;
     /* fpu implementation/revision register (fir) */
     uint32_t fcr0;
+#define FCR0_FREP 29
 #define FCR0_UFRP 28
 #define FCR0_F64 22
 #define FCR0_L 21
@@ -462,6 +463,8 @@ struct CPUMIPSState {
 #define CP0C5_CV         29
 #define CP0C5_EVA        28
 #define CP0C5_MSAEn      27
+#define CP0C5_UFE        9
+#define CP0C5_FRE        8
 #define CP0C5_SBRI       6
 #define CP0C5_UFR        2
 #define CP0C5_NFExists   0
@@ -514,7 +517,7 @@ struct CPUMIPSState {
 #define EXCP_INST_NOTAVAIL 0x2 /* No valid instruction word for BadInstr */
     uint32_t hflags;    /* CPU State */
     /* TMASK defines different execution modes */
-#define MIPS_HFLAG_TMASK  0x15807FF
+#define MIPS_HFLAG_TMASK  0x35807FF
 #define MIPS_HFLAG_MODE   0x00007 /* execution modes                    */
     /* The KSU flags must be the lowest bits in hflags. The flag order
        must be the same as defined for CP0 Status. This allows to use
@@ -561,6 +564,7 @@ struct CPUMIPSState {
 #define MIPS_HFLAG_SBRI  0x400000 /* R6 SDBBP causes RI excpt. in user mode */
 #define MIPS_HFLAG_FBNSLOT 0x800000 /* Forbidden slot                   */
 #define MIPS_HFLAG_MSA   0x1000000
+#define MIPS_HFLAG_FRE   0x2000000 /* FRE enabled */
     target_ulong btarget;        /* Jump / branch target               */
     target_ulong bcond;          /* Branch condition (if needed)       */
 
@@ -843,7 +847,7 @@ static inline void compute_hflags(CPUMIPSState *env)
     env->hflags &= ~(MIPS_HFLAG_COP1X | MIPS_HFLAG_64 | MIPS_HFLAG_CP0 |
                      MIPS_HFLAG_F64 | MIPS_HFLAG_FPU | MIPS_HFLAG_KSU |
                      MIPS_HFLAG_AWRAP | MIPS_HFLAG_DSP | MIPS_HFLAG_DSPR2 |
-                     MIPS_HFLAG_SBRI | MIPS_HFLAG_MSA);
+                     MIPS_HFLAG_SBRI | MIPS_HFLAG_MSA | MIPS_HFLAG_FRE);
     if (!(env->CP0_Status & (1 << CP0St_EXL)) &&
         !(env->CP0_Status & (1 << CP0St_ERL)) &&
         !(env->hflags & MIPS_HFLAG_DM)) {
@@ -924,6 +928,11 @@ static inline void compute_hflags(CPUMIPSState *env)
             env->hflags |= MIPS_HFLAG_MSA;
         }
     }
+    if (env->active_fpu.fcr0 & (1 << FCR0_FREP)) {
+        if (env->CP0_Config5 & (1 << CP0C5_FRE)) {
+            env->hflags |= MIPS_HFLAG_FRE;
+        }
+    }
 }
 
 #ifndef CONFIG_USER_ONLY

target-mips/op_helper.c

@@ -2303,6 +2303,16 @@ target_ulong helper_cfc1(CPUMIPSState *env, uint32_t reg)
             }
         }
         break;
+    case 5:
+        /* FRE Support - read Config5.FRE bit */
+        if (env->active_fpu.fcr0 & (1 << FCR0_FREP)) {
+            if (env->CP0_Config5 & (1 << CP0C5_UFE)) {
+                arg1 = (env->CP0_Config5 >> CP0C5_FRE) & 1;
+            } else {
+                helper_raise_exception(env, EXCP_RI);
+            }
+        }
+        break;
     case 25:
         arg1 = ((env->active_fpu.fcr31 >> 24) & 0xfe) | ((env->active_fpu.fcr31 >> 23) & 0x1);
         break;
@@ -2347,6 +2357,30 @@ void helper_ctc1(CPUMIPSState *env, target_ulong arg1, uint32_t fs, uint32_t rt)
             helper_raise_exception(env, EXCP_RI);
         }
         break;
+    case 5:
+        /* FRE Support - clear Config5.FRE bit */
+        if (!((env->active_fpu.fcr0 & (1 << FCR0_FREP)) && (rt == 0))) {
+            return;
+        }
+        if (env->CP0_Config5 & (1 << CP0C5_UFE)) {
+            env->CP0_Config5 &= ~(1 << CP0C5_FRE);
+            compute_hflags(env);
+        } else {
+            helper_raise_exception(env, EXCP_RI);
+        }
+        break;
+    case 6:
+        /* FRE Support - set Config5.FRE bit */
+        if (!((env->active_fpu.fcr0 & (1 << FCR0_FREP)) && (rt == 0))) {
+            return;
+        }
+        if (env->CP0_Config5 & (1 << CP0C5_UFE)) {
+            env->CP0_Config5 |= (1 << CP0C5_FRE);
+            compute_hflags(env);
+        } else {
+            helper_raise_exception(env, EXCP_RI);
+        }
+        break;
     case 25:
         if ((env->insn_flags & ISA_MIPS32R6) || (arg1 & 0xffffff00)) {
             return;

target-mips/translate_init.c

@@ -622,7 +622,8 @@ static const mips_def_t mips_defs[] =
                        (1 << CP0C3_BI) | (1 << CP0C3_ULRI) | (1U << CP0C3_M),
         .CP0_Config4 = MIPS_CONFIG4 | (0xfc << CP0C4_KScrExist) |
                        (3 << CP0C4_IE) | (1 << CP0C4_M),
-        .CP0_Config5_rw_bitmask = (1 << CP0C5_SBRI),
+        .CP0_Config5_rw_bitmask = (1 << CP0C5_SBRI) | (1 << CP0C5_FRE) |
+                                  (1 << CP0C5_UFE),
         .CP0_LLAddr_rw_bitmask = 0,
         .CP0_LLAddr_shift = 0,
         .SYNCI_Step = 32,
@@ -631,9 +632,9 @@ static const mips_def_t mips_defs[] =
         .CP0_PageGrain = (1 << CP0PG_IEC) | (1 << CP0PG_XIE) |
                          (1U << CP0PG_RIE),
         .CP0_PageGrain_rw_bitmask = 0,
-        .CP1_fcr0 = (1 << FCR0_F64) | (1 << FCR0_L) | (1 << FCR0_W) |
-                    (1 << FCR0_D) | (1 << FCR0_S) | (0x00 << FCR0_PRID) |
-                    (0x0 << FCR0_REV),
+        .CP1_fcr0 = (1 << FCR0_FREP) | (1 << FCR0_F64) | (1 << FCR0_L) |
+                    (1 << FCR0_W) | (1 << FCR0_D) | (1 << FCR0_S) |
+                    (0x00 << FCR0_PRID) | (0x0 << FCR0_REV),
         .SEGBITS = 42,
         /* The architectural limit is 59, but we have hardcoded 36 bit
            in some places...