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linux/arch/mips/kernel/fpu-probe.c
Jiaxun Yang 59649de96f MIPS: Implement ieee754 NAN2008 emulation mode 
Implement ieee754 NAN2008 emulation mode.

When this mode is enabled, kernel will accept ELF file
compiled for both NaN 2008 and NaN legacy, but if hardware
does not have capability to match ELF's NaN mode, __own_fpu
will fail for corresponding thread and fpuemu will then kick
in.

This mode trade performance for correctness, while maintaining
support for both NaN mode regardless of hardware capability.
It is useful for multilib installation that have both types
of binary exist in system.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
2024-07-12 13:09:25 +02:00

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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Processor capabilities determination functions.
*
* Copyright (C) xxxx the Anonymous
* Copyright (C) 1994 - 2006 Ralf Baechle
* Copyright (C) 2003, 2004 Maciej W. Rozycki
* Copyright (C) 2001, 2004, 2011, 2012 MIPS Technologies, Inc.
*/
#include <linux/init.h>
#include <linux/kernel.h>
#include <asm/bugs.h>
#include <asm/cpu.h>
#include <asm/cpu-features.h>
#include <asm/cpu-type.h>
#include <asm/elf.h>
#include <asm/fpu.h>
#include <asm/mipsregs.h>
#include "fpu-probe.h"
/*
* Get the FPU Implementation/Revision.
*/
static inline unsigned long cpu_get_fpu_id(void)
{
unsigned long tmp, fpu_id;
tmp = read_c0_status();
__enable_fpu(FPU_AS_IS);
fpu_id = read_32bit_cp1_register(CP1_REVISION);
write_c0_status(tmp);
return fpu_id;
}
/*
* Check if the CPU has an external FPU.
*/
int __cpu_has_fpu(void)
{
return (cpu_get_fpu_id() & FPIR_IMP_MASK) != FPIR_IMP_NONE;
}
/*
* Determine the FCSR mask for FPU hardware.
*/
static inline void cpu_set_fpu_fcsr_mask(struct cpuinfo_mips *c)
{
unsigned long sr, mask, fcsr, fcsr0, fcsr1;
fcsr = c->fpu_csr31;
mask = FPU_CSR_ALL_X | FPU_CSR_ALL_E | FPU_CSR_ALL_S | FPU_CSR_RM;
sr = read_c0_status();
__enable_fpu(FPU_AS_IS);
fcsr0 = fcsr & mask;
write_32bit_cp1_register(CP1_STATUS, fcsr0);
fcsr0 = read_32bit_cp1_register(CP1_STATUS);
fcsr1 = fcsr | ~mask;
write_32bit_cp1_register(CP1_STATUS, fcsr1);
fcsr1 = read_32bit_cp1_register(CP1_STATUS);
write_32bit_cp1_register(CP1_STATUS, fcsr);
write_c0_status(sr);
c->fpu_msk31 = ~(fcsr0 ^ fcsr1) & ~mask;
}
/*
* Determine the IEEE 754 NaN encodings and ABS.fmt/NEG.fmt execution modes
* supported by FPU hardware.
*/
static void cpu_set_fpu_2008(struct cpuinfo_mips *c)
{
if (c->isa_level & (MIPS_CPU_ISA_M32R1 | MIPS_CPU_ISA_M64R1 |
MIPS_CPU_ISA_M32R2 | MIPS_CPU_ISA_M64R2 |
MIPS_CPU_ISA_M32R5 | MIPS_CPU_ISA_M64R5 |
MIPS_CPU_ISA_M32R6 | MIPS_CPU_ISA_M64R6)) {
unsigned long sr, fir, fcsr, fcsr0, fcsr1;
sr = read_c0_status();
__enable_fpu(FPU_AS_IS);
fir = read_32bit_cp1_register(CP1_REVISION);
if (fir & MIPS_FPIR_HAS2008) {
fcsr = read_32bit_cp1_register(CP1_STATUS);
/*
* MAC2008 toolchain never landed in real world, so
* we're only testing whether it can be disabled and
* don't try to enabled it.
*/
fcsr0 = fcsr & ~(FPU_CSR_ABS2008 | FPU_CSR_NAN2008 |
FPU_CSR_MAC2008);
write_32bit_cp1_register(CP1_STATUS, fcsr0);
fcsr0 = read_32bit_cp1_register(CP1_STATUS);
fcsr1 = fcsr | FPU_CSR_ABS2008 | FPU_CSR_NAN2008;
write_32bit_cp1_register(CP1_STATUS, fcsr1);
fcsr1 = read_32bit_cp1_register(CP1_STATUS);
write_32bit_cp1_register(CP1_STATUS, fcsr);
if (c->isa_level & (MIPS_CPU_ISA_M32R2 |
MIPS_CPU_ISA_M64R2)) {
/*
* The bit for MAC2008 might be reused by R6
* in future, so we only test for R2-R5.
*/
if (fcsr0 & FPU_CSR_MAC2008)
c->options |= MIPS_CPU_MAC_2008_ONLY;
}
if (!(fcsr0 & FPU_CSR_NAN2008))
c->options |= MIPS_CPU_NAN_LEGACY;
if (fcsr1 & FPU_CSR_NAN2008)
c->options |= MIPS_CPU_NAN_2008;
if ((fcsr0 ^ fcsr1) & FPU_CSR_ABS2008)
c->fpu_msk31 &= ~FPU_CSR_ABS2008;
else
c->fpu_csr31 |= fcsr & FPU_CSR_ABS2008;
if ((fcsr0 ^ fcsr1) & FPU_CSR_NAN2008)
c->fpu_msk31 &= ~FPU_CSR_NAN2008;
else
c->fpu_csr31 |= fcsr & FPU_CSR_NAN2008;
} else {
c->options |= MIPS_CPU_NAN_LEGACY;
}
write_c0_status(sr);
} else {
c->options |= MIPS_CPU_NAN_LEGACY;
}
}
/*
* IEEE 754 conformance mode to use. Affects the NaN encoding and the
* ABS.fmt/NEG.fmt execution mode.
*/
static enum { STRICT, EMULATED, LEGACY, STD2008, RELAXED } ieee754 = STRICT;
/*
* Set the IEEE 754 NaN encodings and the ABS.fmt/NEG.fmt execution modes
* to support by the FPU emulator according to the IEEE 754 conformance
* mode selected. Note that "relaxed" straps the emulator so that it
* allows 2008-NaN binaries even for legacy processors.
*/
static void cpu_set_nofpu_2008(struct cpuinfo_mips *c)
{
c->options &= ~(MIPS_CPU_NAN_2008 | MIPS_CPU_NAN_LEGACY);
c->fpu_csr31 &= ~(FPU_CSR_ABS2008 | FPU_CSR_NAN2008);
c->fpu_msk31 &= ~(FPU_CSR_ABS2008 | FPU_CSR_NAN2008);
switch (ieee754) {
case STRICT:
case EMULATED:
if (c->isa_level & (MIPS_CPU_ISA_M32R1 | MIPS_CPU_ISA_M64R1 |
MIPS_CPU_ISA_M32R2 | MIPS_CPU_ISA_M64R2 |
MIPS_CPU_ISA_M32R5 | MIPS_CPU_ISA_M64R5 |
MIPS_CPU_ISA_M32R6 | MIPS_CPU_ISA_M64R6)) {
c->options |= MIPS_CPU_NAN_2008 | MIPS_CPU_NAN_LEGACY;
} else {
c->options |= MIPS_CPU_NAN_LEGACY;
c->fpu_msk31 |= FPU_CSR_ABS2008 | FPU_CSR_NAN2008;
}
break;
case LEGACY:
c->options |= MIPS_CPU_NAN_LEGACY;
c->fpu_msk31 |= FPU_CSR_ABS2008 | FPU_CSR_NAN2008;
break;
case STD2008:
c->options |= MIPS_CPU_NAN_2008;
c->fpu_csr31 |= FPU_CSR_ABS2008 | FPU_CSR_NAN2008;
c->fpu_msk31 |= FPU_CSR_ABS2008 | FPU_CSR_NAN2008;
break;
case RELAXED:
c->options |= MIPS_CPU_NAN_2008 | MIPS_CPU_NAN_LEGACY;
break;
}
}
/*
* Override the IEEE 754 NaN encoding and ABS.fmt/NEG.fmt execution mode
* according to the "ieee754=" parameter.
*/
static void cpu_set_nan_2008(struct cpuinfo_mips *c)
{
switch (ieee754) {
case STRICT:
mips_use_nan_legacy = !!cpu_has_nan_legacy;
mips_use_nan_2008 = !!cpu_has_nan_2008;
break;
case LEGACY:
mips_use_nan_legacy = !!cpu_has_nan_legacy;
mips_use_nan_2008 = !cpu_has_nan_legacy;
break;
case STD2008:
mips_use_nan_legacy = !cpu_has_nan_2008;
mips_use_nan_2008 = !!cpu_has_nan_2008;
break;
case EMULATED:
/* Pretend ABS2008/NAN2008 options are dynamic */
c->fpu_msk31 &= ~(FPU_CSR_NAN2008 | FPU_CSR_ABS2008);
fallthrough;
case RELAXED:
mips_use_nan_legacy = true;
mips_use_nan_2008 = true;
break;
}
}
/*
* IEEE 754 NaN encoding and ABS.fmt/NEG.fmt execution mode override
* settings:
*
* strict: accept binaries that request a NaN encoding supported by the FPU
* legacy: only accept legacy-NaN binaries
* 2008: only accept 2008-NaN binaries
* relaxed: accept any binaries regardless of whether supported by the FPU
*/
static int __init ieee754_setup(char *s)
{
if (!s)
return -1;
else if (!strcmp(s, "strict"))
ieee754 = STRICT;
else if (!strcmp(s, "emulated"))
ieee754 = EMULATED;
else if (!strcmp(s, "legacy"))
ieee754 = LEGACY;
else if (!strcmp(s, "2008"))
ieee754 = STD2008;
else if (!strcmp(s, "relaxed"))
ieee754 = RELAXED;
else
return -1;
if (!(boot_cpu_data.options & MIPS_CPU_FPU))
cpu_set_nofpu_2008(&boot_cpu_data);
cpu_set_nan_2008(&boot_cpu_data);
return 0;
}
early_param("ieee754", ieee754_setup);
/*
* Set the FIR feature flags for the FPU emulator.
*/
static void cpu_set_nofpu_id(struct cpuinfo_mips *c)
{
u32 value;
value = 0;
if (c->isa_level & (MIPS_CPU_ISA_M32R1 | MIPS_CPU_ISA_M64R1 |
MIPS_CPU_ISA_M32R2 | MIPS_CPU_ISA_M64R2 |
MIPS_CPU_ISA_M32R5 | MIPS_CPU_ISA_M64R5 |
MIPS_CPU_ISA_M32R6 | MIPS_CPU_ISA_M64R6))
value |= MIPS_FPIR_D | MIPS_FPIR_S;
if (c->isa_level & (MIPS_CPU_ISA_M32R2 | MIPS_CPU_ISA_M64R2 |
MIPS_CPU_ISA_M32R5 | MIPS_CPU_ISA_M64R5 |
MIPS_CPU_ISA_M32R6 | MIPS_CPU_ISA_M64R6))
value |= MIPS_FPIR_F64 | MIPS_FPIR_L | MIPS_FPIR_W;
if (c->options & MIPS_CPU_NAN_2008)
value |= MIPS_FPIR_HAS2008;
c->fpu_id = value;
}
/* Determined FPU emulator mask to use for the boot CPU with "nofpu". */
static unsigned int mips_nofpu_msk31;
/*
* Set options for FPU hardware.
*/
void cpu_set_fpu_opts(struct cpuinfo_mips *c)
{
c->fpu_id = cpu_get_fpu_id();
mips_nofpu_msk31 = c->fpu_msk31;
if (c->isa_level & (MIPS_CPU_ISA_M32R1 | MIPS_CPU_ISA_M64R1 |
MIPS_CPU_ISA_M32R2 | MIPS_CPU_ISA_M64R2 |
MIPS_CPU_ISA_M32R5 | MIPS_CPU_ISA_M64R5 |
MIPS_CPU_ISA_M32R6 | MIPS_CPU_ISA_M64R6)) {
if (c->fpu_id & MIPS_FPIR_3D)
c->ases |= MIPS_ASE_MIPS3D;
if (c->fpu_id & MIPS_FPIR_UFRP)
c->options |= MIPS_CPU_UFR;
if (c->fpu_id & MIPS_FPIR_FREP)
c->options |= MIPS_CPU_FRE;
}
cpu_set_fpu_fcsr_mask(c);
cpu_set_fpu_2008(c);
cpu_set_nan_2008(c);
}
/*
* Set options for the FPU emulator.
*/
void cpu_set_nofpu_opts(struct cpuinfo_mips *c)
{
c->options &= ~MIPS_CPU_FPU;
c->fpu_msk31 = mips_nofpu_msk31;
cpu_set_nofpu_2008(c);
cpu_set_nan_2008(c);
cpu_set_nofpu_id(c);
}
int mips_fpu_disabled;
static int __init fpu_disable(char *s)
{
cpu_set_nofpu_opts(&boot_cpu_data);
mips_fpu_disabled = 1;
return 1;
}
__setup("nofpu", fpu_disable);
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