openwrt/target/linux/generic/patches-3.10/304-mips_disable_fpu.patch

MIPS: allow disabling the kernel FPU emulator

This patch allows turning off the in-kernel Algorithmics
FPU emulator support, which allows one to save a couple of
precious blocks on an embedded system.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
--
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -976,6 +976,17 @@ config I8259
 config MIPS_BONITO64
 	bool
 
+config MIPS_FPU_EMU
+	bool "Enable FPU emulation"
+	default y
+	help
+	   This option allows building a kernel with or without the Algorithmics
+	   FPU emulator enabled. Turning off this option results in a kernel which
+	   does not catch floating operations exceptions. Make sure that your toolchain
+	   is configured to enable software floating point emulation in that case.
+		
+	   If unsure say Y here.
+
 config MIPS_MSC
 	bool
 
--- a/arch/mips/math-emu/Makefile
+++ b/arch/mips/math-emu/Makefile
@@ -2,10 +2,11 @@
 # Makefile for the Linux/MIPS kernel FPU emulation.
 #
 
-obj-y	:= cp1emu.o ieee754m.o ieee754d.o ieee754dp.o ieee754sp.o ieee754.o \
+obj-y	:= kernel_linkage.o dsemul.o cp1emu.o
+obj-$(CONFIG_MIPS_FPU_EMU)	+= ieee754m.o ieee754d.o ieee754dp.o ieee754sp.o ieee754.o \
 	   ieee754xcpt.o dp_frexp.o dp_modf.o dp_div.o dp_mul.o dp_sub.o \
 	   dp_add.o dp_fsp.o dp_cmp.o dp_logb.o dp_scalb.o dp_simple.o \
 	   dp_tint.o dp_fint.o dp_tlong.o dp_flong.o sp_frexp.o sp_modf.o \
 	   sp_div.o sp_mul.o sp_sub.o sp_add.o sp_fdp.o sp_cmp.o sp_logb.o \
 	   sp_scalb.o sp_simple.o sp_tint.o sp_fint.o sp_tlong.o sp_flong.o \
-	   dp_sqrt.o sp_sqrt.o kernel_linkage.o dsemul.o
+	   dp_sqrt.o sp_sqrt.o
--- a/arch/mips/math-emu/cp1emu.c
+++ b/arch/mips/math-emu/cp1emu.c
@@ -59,7 +59,11 @@
 #define __mips 4
 
 /* Function which emulates a floating point instruction. */
+#ifdef CONFIG_DEBUG_FS
+DEFINE_PER_CPU(struct mips_fpu_emulator_stats, fpuemustats);
+#endif
 
+#ifdef CONFIG_MIPS_FPU_EMU
 static int fpu_emu(struct pt_regs *, struct mips_fpu_struct *,
 	mips_instruction);
 
@@ -70,10 +74,6 @@ static int fpux_emu(struct pt_regs *,
 
 /* Further private data for which no space exists in mips_fpu_struct */
 
-#ifdef CONFIG_DEBUG_FS
-DEFINE_PER_CPU(struct mips_fpu_emulator_stats, fpuemustats);
-#endif
-
 /* Control registers */
 
 #define FPCREG_RID	0	/* $0  = revision id */
@@ -82,11 +82,15 @@ DEFINE_PER_CPU(struct mips_fpu_emulator_
 /* Determine rounding mode from the RM bits of the FCSR */
 #define modeindex(v) ((v) & FPU_CSR_RM)
 
+#endif /* CONFIG_MIPS_FPU_EMU */
+
 /* microMIPS bitfields */
 #define MM_POOL32A_MINOR_MASK	0x3f
 #define MM_POOL32A_MINOR_SHIFT	0x6
 #define MM_MIPS32_COND_FC	0x30
 
+#ifdef CONFIG_MIPS_FPU_EMU
+
 /* Convert Mips rounding mode (0..3) to IEEE library modes. */
 static const unsigned char ieee_rm[4] = {
 	[FPU_CSR_RN] = IEEE754_RN,
@@ -116,9 +120,13 @@ static const unsigned int fpucondbit[8] 
 };
 #endif
 
+#endif /* CONFIG_MIPS_FPU_EMU */
+
 /* (microMIPS) Convert 16-bit register encoding to 32-bit register encoding. */
 static const unsigned int reg16to32map[8] = {16, 17, 2, 3, 4, 5, 6, 7};
 
+#ifdef CONFIG_MIPS_FPU_EMU
+
 /* (microMIPS) Convert certain microMIPS instructions to MIPS32 format. */
 static const int sd_format[] = {16, 17, 0, 0, 0, 0, 0, 0};
 static const int sdps_format[] = {16, 17, 22, 0, 0, 0, 0, 0};
@@ -463,6 +471,8 @@ static int microMIPS32_to_MIPS32(union m
 	return 0;
 }
 
+#endif /* CONFIG_MIPS_FPU_EMU */
+
 int mm_isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,
 		     unsigned long *contpc)
 {
@@ -667,6 +677,8 @@ int mm_isBranchInstr(struct pt_regs *reg
 	return 0;
 }
 
+#ifdef CONFIG_MIPS_FPU_EMU
+
 /*
  * Redundant with logic already in kernel/branch.c,
  * embedded in compute_return_epc.  At some point,
@@ -2102,7 +2114,6 @@ int fpu_emulator_cop1Handler(struct pt_r
 
 	return sig;
 }
-
 #ifdef CONFIG_DEBUG_FS
 
 static int fpuemu_stat_get(void *data, u64 *val)
@@ -2151,4 +2162,11 @@ static int __init debugfs_fpuemu(void)
 	return 0;
 }
 __initcall(debugfs_fpuemu);
-#endif
+#endif /* CONFIG_DEBUGFS */
+#else
+int fpu_emulator_cop1Handler(struct pt_regs *xcp, struct mips_fpu_struct *ctx,
+        int has_fpu, void *__user *fault_addr)
+{
+	return 0;
+}
+#endif /* CONFIG_MIPS_FPU_EMU */
--- a/arch/mips/math-emu/dsemul.c
+++ b/arch/mips/math-emu/dsemul.c
@@ -119,6 +119,7 @@ int mips_dsemul(struct pt_regs *regs, mi
 	return SIGILL;		/* force out of emulation loop */
 }
 
+#ifdef CONFIG_MIPS_FPU_EMU
 int do_dsemulret(struct pt_regs *xcp)
 {
 	struct emuframe __user *fr;
@@ -182,3 +183,9 @@ int do_dsemulret(struct pt_regs *xcp)
 
 	return 1;
 }
+#else
+int do_dsemulret(struct pt_regs *xcp)
+{
+	return 0;
+}
+#endif /* CONFIG_MIPS_FPU_EMU */
--- a/arch/mips/math-emu/kernel_linkage.c
+++ b/arch/mips/math-emu/kernel_linkage.c
@@ -29,6 +29,7 @@
 
 #define SIGNALLING_NAN 0x7ff800007ff80000LL
 
+#ifdef CONFIG_MIPS_FPU_EMU
 void fpu_emulator_init_fpu(void)
 {
 	static int first = 1;
@@ -112,4 +113,36 @@ int fpu_emulator_restore_context32(struc
 
 	return err;
 }
-#endif
+#endif	/* CONFIG_64BIT */
+#else
+
+void fpu_emulator_init_fpu(void)
+{
+	printk(KERN_INFO "FPU emulator disabled, make sure your toolchain"
+		"was compiled with software floating point support (soft-float)\n");
+	return;
+}
+
+int fpu_emulator_save_context(struct sigcontext __user *sc)
+{
+	return 0;
+}
+
+int fpu_emulator_restore_context(struct sigcontext __user *sc)
+{
+	return 0;
+}
+
+int fpu_emulator_save_context32(struct sigcontext32 __user *sc)
+{
+	return 0;
+}
+
+int fpu_emulator_restore_context32(struct sigcontext32 __user *sc)
+{
+	return 0;
+}
+
+#ifdef CONFIG_64BIT
+#endif	/* CONFIG_64BIT */
+#endif /* CONFIG_MIPS_FPU_EMU */