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authorVincent Chen <vincentc@andestech.com>2018-11-22 11:14:36 +0800
committerGreentime Hu <greentime@andestech.com>2018-11-22 18:13:27 +0800
commit44e92e0364adfd7b6759084e02a550d06336d896 (patch)
tree4fb8af79a5ce25f9467bdc22f44e67f6ae42b6d6 /arch/nds32
parentnds32: Support FP emulation (diff)
downloadlinux-dev-44e92e0364adfd7b6759084e02a550d06336d896.tar.xz
linux-dev-44e92e0364adfd7b6759084e02a550d06336d896.zip
nds32: support denormalized result through FP emulator
Currently, the nds32 FPU dose not support the arithmetic of denormalized number. When the nds32 FPU finds the result of the instruction is a denormlized number, the nds32 FPU considers it to be an underflow condition and rounds the result to an appropriate number. It may causes some loss of precision. This commit proposes a solution to re-execute the instruction by the FPU emulator to enhance the precision. To transfer calculations from user space to kernel space, this feature will enable the underflow exception trap by default. Enabling this feature may cause some side effects: 1. Performance loss due to extra FPU exception 2. Need another scheme to control real underflow trap A new parameter, UDF_trap, which is belong to FPU context is used to control underflow trap. User can configure this feature via CONFIG_SUPPORT_DENORMAL_ARITHMETIC Signed-off-by: Vincent Chen <vincentc@andestech.com> Acked-by: Greentime Hu <greentime@andestech.com> Signed-off-by: Greentime Hu <greentime@andestech.com>
Diffstat (limited to 'arch/nds32')
-rw-r--r--arch/nds32/Kconfig.cpu13
-rw-r--r--arch/nds32/include/asm/elf.h11
-rw-r--r--arch/nds32/include/asm/fpu.h11
-rw-r--r--arch/nds32/include/asm/syscalls.h1
-rw-r--r--arch/nds32/include/uapi/asm/auxvec.h7
-rw-r--r--arch/nds32/include/uapi/asm/sigcontext.h9
-rw-r--r--arch/nds32/include/uapi/asm/udftrap.h13
-rw-r--r--arch/nds32/include/uapi/asm/unistd.h2
-rw-r--r--arch/nds32/kernel/fpu.c25
-rw-r--r--arch/nds32/kernel/sys_nds32.c32
-rw-r--r--arch/nds32/math-emu/fpuemu.c5
11 files changed, 125 insertions, 4 deletions
diff --git a/arch/nds32/Kconfig.cpu b/arch/nds32/Kconfig.cpu
index bb06a1b7eef0..6482ed877f97 100644
--- a/arch/nds32/Kconfig.cpu
+++ b/arch/nds32/Kconfig.cpu
@@ -28,6 +28,19 @@ config LAZY_FPU
For nomal case, say Y.
+config SUPPORT_DENORMAL_ARITHMETIC
+ bool "Denormal arithmetic support"
+ depends on FPU
+ default n
+ help
+ Say Y here to enable arithmetic of denormalized number. Enabling
+ this feature can enhance the precision for tininess number.
+ However, performance loss in float pointe calculations is
+ possibly significant due to additional FPU exception.
+
+ If the calculated tolerance for tininess number is not critical,
+ say N to prevent performance loss.
+
config HWZOL
bool "hardware zero overhead loop support"
depends on CPU_D10 || CPU_D15
diff --git a/arch/nds32/include/asm/elf.h b/arch/nds32/include/asm/elf.h
index f5f9cf7e0544..95f3ea253e4c 100644
--- a/arch/nds32/include/asm/elf.h
+++ b/arch/nds32/include/asm/elf.h
@@ -9,6 +9,7 @@
*/
#include <asm/ptrace.h>
+#include <asm/fpu.h>
typedef unsigned long elf_greg_t;
typedef unsigned long elf_freg_t[3];
@@ -159,8 +160,18 @@ struct elf32_hdr;
#endif
+
+#if IS_ENABLED(CONFIG_FPU)
+#define FPU_AUX_ENT NEW_AUX_ENT(AT_FPUCW, FPCSR_INIT)
+#else
+#define FPU_AUX_ENT NEW_AUX_ENT(AT_IGNORE, 0)
+#endif
+
#define ARCH_DLINFO \
do { \
+ /* Optional FPU initialization */ \
+ FPU_AUX_ENT; \
+ \
NEW_AUX_ENT(AT_SYSINFO_EHDR, \
(elf_addr_t)current->mm->context.vdso); \
} while (0)
diff --git a/arch/nds32/include/asm/fpu.h b/arch/nds32/include/asm/fpu.h
index 9b1107b58e23..019f1bcfc5ee 100644
--- a/arch/nds32/include/asm/fpu.h
+++ b/arch/nds32/include/asm/fpu.h
@@ -28,7 +28,18 @@ extern int do_fpuemu(struct pt_regs *regs, struct fpu_struct *fpu);
#define sNAN64 0xFFFFFFFFFFFFFFFFULL
#define sNAN32 0xFFFFFFFFUL
+#if IS_ENABLED(CONFIG_SUPPORT_DENORMAL_ARITHMETIC)
+/*
+ * Denormalized number is unsupported by nds32 FPU. Hence the operation
+ * is treated as underflow cases when the final result is a denormalized
+ * number. To enhance precision, underflow exception trap should be
+ * enabled by default and kerenl will re-execute it by fpu emulator
+ * when getting underflow exception.
+ */
+#define FPCSR_INIT FPCSR_mskUDFE
+#else
#define FPCSR_INIT 0x0UL
+#endif
extern const struct fpu_struct init_fpuregs;
diff --git a/arch/nds32/include/asm/syscalls.h b/arch/nds32/include/asm/syscalls.h
index 78778ecff60c..da32101b455d 100644
--- a/arch/nds32/include/asm/syscalls.h
+++ b/arch/nds32/include/asm/syscalls.h
@@ -7,6 +7,7 @@
asmlinkage long sys_cacheflush(unsigned long addr, unsigned long len, unsigned int op);
asmlinkage long sys_fadvise64_64_wrapper(int fd, int advice, loff_t offset, loff_t len);
asmlinkage long sys_rt_sigreturn_wrapper(void);
+asmlinkage long sys_udftrap(int option);
#include <asm-generic/syscalls.h>
diff --git a/arch/nds32/include/uapi/asm/auxvec.h b/arch/nds32/include/uapi/asm/auxvec.h
index 56043ce4972f..2d3213f5e595 100644
--- a/arch/nds32/include/uapi/asm/auxvec.h
+++ b/arch/nds32/include/uapi/asm/auxvec.h
@@ -4,6 +4,13 @@
#ifndef __ASM_AUXVEC_H
#define __ASM_AUXVEC_H
+/*
+ * This entry gives some information about the FPU initialization
+ * performed by the kernel.
+ */
+#define AT_FPUCW 18 /* Used FPU control word. */
+
+
/* VDSO location */
#define AT_SYSINFO_EHDR 33
diff --git a/arch/nds32/include/uapi/asm/sigcontext.h b/arch/nds32/include/uapi/asm/sigcontext.h
index 1257a78e3ae1..58afc416473e 100644
--- a/arch/nds32/include/uapi/asm/sigcontext.h
+++ b/arch/nds32/include/uapi/asm/sigcontext.h
@@ -12,6 +12,15 @@
struct fpu_struct {
unsigned long long fd_regs[32];
unsigned long fpcsr;
+ /*
+ * UDF_trap is used to recognize whether underflow trap is enabled
+ * or not. When UDF_trap == 1, this process will be traped and then
+ * get a SIGFPE signal when encountering an underflow exception.
+ * UDF_trap is only modified through setfputrap syscall. Therefore,
+ * UDF_trap needn't be saved or loaded to context in each context
+ * switch.
+ */
+ unsigned long UDF_trap;
};
struct zol_struct {
diff --git a/arch/nds32/include/uapi/asm/udftrap.h b/arch/nds32/include/uapi/asm/udftrap.h
new file mode 100644
index 000000000000..433f79d679c0
--- /dev/null
+++ b/arch/nds32/include/uapi/asm/udftrap.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) 2005-2018 Andes Technology Corporation */
+#ifndef _ASM_SETFPUTRAP
+#define _ASM_SETFPUTRAP
+
+/*
+ * Options for setfputrap system call
+ */
+#define DISABLE_UDFTRAP 0 /* disable underflow exception trap */
+#define ENABLE_UDFTRAP 1 /* enable undeflos exception trap */
+#define GET_UDFTRAP 2 /* only get undeflos exception trap status */
+
+#endif /* _ASM_CACHECTL */
diff --git a/arch/nds32/include/uapi/asm/unistd.h b/arch/nds32/include/uapi/asm/unistd.h
index 603e826e0449..c2c3a3e34083 100644
--- a/arch/nds32/include/uapi/asm/unistd.h
+++ b/arch/nds32/include/uapi/asm/unistd.h
@@ -9,4 +9,6 @@
/* Additional NDS32 specific syscalls. */
#define __NR_cacheflush (__NR_arch_specific_syscall)
+#define __NR_udftrap (__NR_arch_specific_syscall + 1)
__SYSCALL(__NR_cacheflush, sys_cacheflush)
+__SYSCALL(__NR_udftrap, sys_udftrap)
diff --git a/arch/nds32/kernel/fpu.c b/arch/nds32/kernel/fpu.c
index 2942df6f93e6..fddd40c7a16f 100644
--- a/arch/nds32/kernel/fpu.c
+++ b/arch/nds32/kernel/fpu.c
@@ -12,7 +12,10 @@
const struct fpu_struct init_fpuregs = {
.fd_regs = {[0 ... 31] = sNAN64},
- .fpcsr = FPCSR_INIT
+ .fpcsr = FPCSR_INIT,
+#if IS_ENABLED(CONFIG_SUPPORT_DENORMAL_ARITHMETIC)
+ .UDF_trap = 0
+#endif
};
void save_fpu(struct task_struct *tsk)
@@ -174,6 +177,9 @@ inline void do_fpu_context_switch(struct pt_regs *regs)
} else {
/* First time FPU user. */
load_fpu(&init_fpuregs);
+#if IS_ENABLED(CONFIG_SUPPORT_DENORMAL_ARITHMETIC)
+ current->thread.fpu.UDF_trap = init_fpuregs.UDF_trap;
+#endif
set_used_math();
}
@@ -183,10 +189,12 @@ inline void fill_sigfpe_signo(unsigned int fpcsr, int *signo)
{
if (fpcsr & FPCSR_mskOVFT)
*signo = FPE_FLTOVF;
- else if (fpcsr & FPCSR_mskIVOT)
- *signo = FPE_FLTINV;
+#ifndef CONFIG_SUPPORT_DENORMAL_ARITHMETIC
else if (fpcsr & FPCSR_mskUDFT)
*signo = FPE_FLTUND;
+#endif
+ else if (fpcsr & FPCSR_mskIVOT)
+ *signo = FPE_FLTINV;
else if (fpcsr & FPCSR_mskDBZT)
*signo = FPE_FLTDIV;
else if (fpcsr & FPCSR_mskIEXT)
@@ -197,11 +205,20 @@ inline void handle_fpu_exception(struct pt_regs *regs)
{
unsigned int fpcsr;
int si_code = 0, si_signo = SIGFPE;
+#if IS_ENABLED(CONFIG_SUPPORT_DENORMAL_ARITHMETIC)
+ unsigned long redo_except = FPCSR_mskDNIT|FPCSR_mskUDFT;
+#else
+ unsigned long redo_except = FPCSR_mskDNIT;
+#endif
lose_fpu();
fpcsr = current->thread.fpu.fpcsr;
- if (fpcsr & FPCSR_mskDNIT) {
+ if (fpcsr & redo_except) {
+#if IS_ENABLED(CONFIG_SUPPORT_DENORMAL_ARITHMETIC)
+ if (fpcsr & FPCSR_mskUDFT)
+ current->thread.fpu.fpcsr &= ~FPCSR_mskIEX;
+#endif
si_signo = do_fpuemu(regs, &current->thread.fpu);
fpcsr = current->thread.fpu.fpcsr;
if (!si_signo)
diff --git a/arch/nds32/kernel/sys_nds32.c b/arch/nds32/kernel/sys_nds32.c
index 9de93ab4c52b..0835277636ce 100644
--- a/arch/nds32/kernel/sys_nds32.c
+++ b/arch/nds32/kernel/sys_nds32.c
@@ -6,6 +6,8 @@
#include <asm/cachectl.h>
#include <asm/proc-fns.h>
+#include <asm/udftrap.h>
+#include <asm/fpu.h>
SYSCALL_DEFINE6(mmap2, unsigned long, addr, unsigned long, len,
unsigned long, prot, unsigned long, flags,
@@ -48,3 +50,33 @@ SYSCALL_DEFINE3(cacheflush, unsigned int, start, unsigned int, end, int, cache)
return 0;
}
+
+SYSCALL_DEFINE1(udftrap, int, option)
+{
+#if IS_ENABLED(CONFIG_SUPPORT_DENORMAL_ARITHMETIC)
+ int old_udftrap;
+
+ if (!used_math()) {
+ load_fpu(&init_fpuregs);
+ current->thread.fpu.UDF_trap = init_fpuregs.UDF_trap;
+ set_used_math();
+ }
+
+ old_udftrap = current->thread.fpu.UDF_trap;
+ switch (option) {
+ case DISABLE_UDFTRAP:
+ current->thread.fpu.UDF_trap = 0;
+ break;
+ case ENABLE_UDFTRAP:
+ current->thread.fpu.UDF_trap = FPCSR_mskUDFE;
+ break;
+ case GET_UDFTRAP:
+ break;
+ default:
+ return -EINVAL;
+ }
+ return old_udftrap;
+#else
+ return -ENOTSUPP;
+#endif
+}
diff --git a/arch/nds32/math-emu/fpuemu.c b/arch/nds32/math-emu/fpuemu.c
index 2a01333d6e5f..75cf1643fa78 100644
--- a/arch/nds32/math-emu/fpuemu.c
+++ b/arch/nds32/math-emu/fpuemu.c
@@ -304,7 +304,12 @@ static int fpu_emu(struct fpu_struct *fpu_reg, unsigned long insn)
/*
* If an exception is required, generate a tidy SIGFPE exception.
*/
+#if IS_ENABLED(CONFIG_SUPPORT_DENORMAL_ARITHMETIC)
+ if (((fpu_reg->fpcsr << 5) & fpu_reg->fpcsr & FPCSR_mskALLE_NO_UDFE) ||
+ ((fpu_reg->fpcsr & FPCSR_mskUDF) && (fpu_reg->UDF_trap)))
+#else
if ((fpu_reg->fpcsr << 5) & fpu_reg->fpcsr & FPCSR_mskALLE)
+#endif
return SIGFPE;
return 0;
}