MIPS: math-emu: Define IEEE 754-2008 feature control bits

Define IEEE 754-2008 feature control bits: FIR.HAS2008, FCSR.ABS2008 and
FCSR.NAN2008, and update the `_ieee754_csr' structure accordingly.

For completeness define FIR.UFRP too.
Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9709/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/mipsregs.h

@@ -708,6 +708,8 @@
 #define MIPS_FPIR_W		(_ULCAST_(1) << 20)
 #define MIPS_FPIR_L		(_ULCAST_(1) << 21)
 #define MIPS_FPIR_F64		(_ULCAST_(1) << 22)
+#define MIPS_FPIR_HAS2008	(_ULCAST_(1) << 23)
+#define MIPS_FPIR_UFRP		(_ULCAST_(1) << 28)
 #define MIPS_FPIR_FREP		(_ULCAST_(1) << 29)
 
 /*
@@ -765,10 +767,13 @@
 #define FPU_CSR_COND7	(_ULCAST_(1) << FPU_CSR_COND7_S)
 
 /*
- * Bits 18 - 20 of the FPU Status Register will be read as 0,
+ * Bits 22:20 of the FPU Status Register will be read as 0,
  * and should be written as zero.
  */
-#define FPU_CSR_RSVD	0x001c0000
+#define FPU_CSR_RSVD	(_ULCAST_(7) << 20)
+
+#define FPU_CSR_ABS2008	(_ULCAST_(1) << 19)
+#define FPU_CSR_NAN2008	(_ULCAST_(1) << 18)
 
 /*
  * X the exception cause indicator

arch/mips/math-emu/cp1emu.c

@@ -919,8 +919,9 @@ static inline void cop1_ctc(struct pt_regs *xcp, struct mips_fpu_struct *ctx,
 		pr_debug("%p gpr[%d]->csr=%08x\n",
 			 (void *)xcp->cp0_epc, MIPSInst_RT(ir), value);
 
-		/* Don't write reserved bits.  */
-		fcr31 = value & ~FPU_CSR_RSVD;
+		/* Don't write unsupported bits.  */
+		fcr31 = value &
+			~(FPU_CSR_RSVD | FPU_CSR_ABS2008 | FPU_CSR_NAN2008);
 		break;
 
 	case FPCREG_FENR:

arch/mips/math-emu/ieee754.h

@@ -130,15 +130,17 @@ enum {
  * The control status register
  */
 struct _ieee754_csr {
-	__BITFIELD_FIELD(unsigned pad0:7,
-	__BITFIELD_FIELD(unsigned nod:1,	/* set 1 for no denormalised numbers */
-	__BITFIELD_FIELD(unsigned c:1,		/* condition */
-	__BITFIELD_FIELD(unsigned pad1:5,
+	__BITFIELD_FIELD(unsigned fcc:7,	/* condition[7:1] */
+	__BITFIELD_FIELD(unsigned nod:1,	/* set 1 for no denormals */
+	__BITFIELD_FIELD(unsigned c:1,		/* condition[0] */
+	__BITFIELD_FIELD(unsigned pad0:3,
+	__BITFIELD_FIELD(unsigned abs2008:1,	/* IEEE 754-2008 ABS/NEG.fmt */
+	__BITFIELD_FIELD(unsigned nan2008:1,	/* IEEE 754-2008 NaN mode */
 	__BITFIELD_FIELD(unsigned cx:6,		/* exceptions this operation */
 	__BITFIELD_FIELD(unsigned mx:5,		/* exception enable  mask */
 	__BITFIELD_FIELD(unsigned sx:5,		/* exceptions total */
 	__BITFIELD_FIELD(unsigned rm:2,		/* current rounding mode */
-	;))))))))
+	;))))))))))
 };
 #define ieee754_csr (*(struct _ieee754_csr *)(&current->thread.fpu.fcr31))