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Unverified Commit 9411ec60 authored by Alan Kao's avatar Alan Kao Committed by Palmer Dabbelt
Browse files

Auto-detect whether a FPU exists 



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: default avatarAlan 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: default avatarPalmer Dabbelt <palmer@sifive.com>
parent 9671f706

arch/riscv/include/asm/switch_to.h

+4 −4
Original line number Diff line number Diff line
@@ -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 *,
@@ -72,6 +71,7 @@ extern struct task_struct *__switch_to(struct task_struct *, 
do {							\

	struct task_struct *__prev = (prev);		\

	struct task_struct *__next = (next);		\

	if (has_fpu)					\

		__switch_to_aux(__prev, __next);	\

	((last) = __switch_to(__prev, __next));		\

} while (0)

arch/riscv/kernel/cpufeature.c

+8 −0
Original line number Diff line number Diff line
@@ -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

}

arch/riscv/kernel/process.c

+3 −1
Original line number Diff line number Diff line
@@ -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);

arch/riscv/kernel/signal.c

+4 −2
Original line number Diff line number Diff line
@@ -98,6 +98,7 @@ 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. */

	if (has_fpu)

		err |= restore_fp_state(regs, &sc->sc_fpregs);

	return err;

}
@@ -150,6 +151,7 @@ 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. */

	if (has_fpu)

		err |= save_fp_state(regs, &sc->sc_fpregs);

	return err;

}