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Auto-detect whether a FPU exists

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We expect that a kernel with CONFIG_FPU=y can still support no-FPU
machines. To do so, the kernel should first examine the existence of a
FPU, then do nothing if a FPU does exist; otherwise, it should
disable/bypass all FPU-related functions.

In this patch, a new global variable, has_fpu, is created and determined
when parsing the hardware capability from device tree during booting.
This variable is used in those FPU-related functions.

Signed-off-by: Alan Kao <alankao@andestech.com>
Cc: Greentime Hu <greentime@andestech.com>
Cc: Vincent Chen <vincentc@andestech.com>
Cc: Zong Li <zong@andestech.com>
Cc: Nick Hu <nickhu@andestech.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
This commit is contained in:
Alan Kao 2018-10-09 10:18:34 +08:00 committed by Palmer Dabbelt
parent 9671f70614
commit 9411ec60c2
No known key found for this signature in database
GPG key ID: EF4CA1502CCBAB41
4 changed files with 19 additions and 7 deletions
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8
arch/riscv/include/asm/switch_to.h
View file

@ -56,13 +56,12 @@ static inline void __switch_to_aux(struct task_struct *prev,
fstate_restore(next, task_pt_regs(next));
}
#define DEFAULT_SSTATUS (SR_SPIE | SR_FS_INITIAL)
extern bool has_fpu;
#else
#define has_fpu false
#define fstate_save(task, regs) do { } while (0)
#define fstate_restore(task, regs) do { } while (0)
#define __switch_to_aux(__prev, __next) do { } while (0)
#define DEFAULT_SSTATUS (SR_SPIE | SR_FS_OFF)
#endif
extern struct task_struct *__switch_to(struct task_struct *,
@ -72,7 +71,8 @@ extern struct task_struct *__switch_to(struct task_struct *,
do { \
struct task_struct *__prev = (prev); \
struct task_struct *__next = (next); \
__switch_to_aux(__prev, __next); \
if (has_fpu) \
__switch_to_aux(__prev, __next); \
((last) = __switch_to(__prev, __next)); \
} while (0)

8
arch/riscv/kernel/cpufeature.c
View file

@ -22,6 +22,9 @@
#include <asm/hwcap.h>
unsigned long elf_hwcap __read_mostly;
#ifdef CONFIG_FPU
bool has_fpu __read_mostly;
#endif
void riscv_fill_hwcap(void)
{
@ -58,4 +61,9 @@ void riscv_fill_hwcap(void)
elf_hwcap |= isa2hwcap[(unsigned char)(isa[i])];
pr_info("elf_hwcap is 0x%lx", elf_hwcap);
#ifdef CONFIG_FPU
if (elf_hwcap & (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D))
has_fpu = true;
#endif
}

4
arch/riscv/kernel/process.c
View file

@ -76,7 +76,9 @@ void show_regs(struct pt_regs *regs)
void start_thread(struct pt_regs *regs, unsigned long pc,
unsigned long sp)
{
regs->sstatus = DEFAULT_SSTATUS;
regs->sstatus = SR_SPIE;
if (has_fpu)
regs->sstatus |= SR_FS_INITIAL;
regs->sepc = pc;
regs->sp = sp;
set_fs(USER_DS);

6
arch/riscv/kernel/signal.c
View file

@ -98,7 +98,8 @@ static long restore_sigcontext(struct pt_regs *regs,
/* sc_regs is structured the same as the start of pt_regs */
err = __copy_from_user(regs, &sc->sc_regs, sizeof(sc->sc_regs));
/* Restore the floating-point state. */
err |= restore_fp_state(regs, &sc->sc_fpregs);
if (has_fpu)
err |= restore_fp_state(regs, &sc->sc_fpregs);
return err;
}
@ -150,7 +151,8 @@ static long setup_sigcontext(struct rt_sigframe __user *frame,
/* sc_regs is structured the same as the start of pt_regs */
err = __copy_to_user(&sc->sc_regs, regs, sizeof(sc->sc_regs));
/* Save the floating-point state. */
err |= save_fp_state(regs, &sc->sc_fpregs);
if (has_fpu)
err |= save_fp_state(regs, &sc->sc_fpregs);
return err;
}