Messages in this thread Patch in this message |  | | From | Alan Kao <> | Subject | [PATCH v4 5/5] Auto-detect whether a FPU exists | Date | Wed, 8 Aug 2018 11:24:45 +0800 |
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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, no_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> --- arch/riscv/include/asm/hwcap.h | 3 +++ arch/riscv/include/asm/switch_to.h | 13 ++++++++++++- arch/riscv/kernel/cpufeature.c | 11 +++++++++++ arch/riscv/kernel/signal.c | 6 ++++++ 4 files changed, 32 insertions(+), 1 deletion(-)
diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h index 8a4ed7bbcbea..1b870086a869 100644 --- a/arch/riscv/include/asm/hwcap.h +++ b/arch/riscv/include/asm/hwcap.h @@ -33,5 +33,8 @@ enum { }; extern unsigned long elf_hwcap; +#ifdef CONFIG_FPU +extern bool no_fpu; +#endif #endif #endif diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h index 093050b03543..7278e3eb7a70 100644 --- a/arch/riscv/include/asm/switch_to.h +++ b/arch/riscv/include/asm/switch_to.h @@ -17,6 +17,7 @@ #include <asm/processor.h> #include <asm/ptrace.h> #include <asm/csr.h> +#include <asm/hwcap.h> #ifdef CONFIG_FPU extern void __fstate_save(struct task_struct *save_to); @@ -30,6 +31,9 @@ static inline void __fstate_clean(struct pt_regs *regs) static inline void fstate_save(struct task_struct *task, struct pt_regs *regs) { + if (unlikely(no_fpu)) + return; + if ((regs->sstatus & SR_FS) == SR_FS_DIRTY) { __fstate_save(task); __fstate_clean(regs); @@ -39,6 +43,9 @@ static inline void fstate_save(struct task_struct *task, static inline void fstate_restore(struct task_struct *task, struct pt_regs *regs) { + if (unlikely(no_fpu)) + return; + if ((regs->sstatus & SR_FS) != SR_FS_OFF) { __fstate_restore(task); __fstate_clean(regs); @@ -50,13 +57,17 @@ static inline void __switch_to_aux(struct task_struct *prev, { struct pt_regs *regs; + if (unlikely(no_fpu)) + return; + regs = task_pt_regs(prev); if (unlikely(regs->sstatus & SR_SD)) fstate_save(prev, regs); fstate_restore(next, task_pt_regs(next)); } -#define DEFAULT_SSTATUS (SR_SPIE | SR_FS_INITIAL) +#define DEFAULT_SSTATUS \ + ((unlikely(no_fpu)) ? (SR_SPIE | SR_FS_OFF) : (SR_SPIE | SR_FS_INITIAL)) #else #define fstate_save(task, regs) do { } while (0) diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c index 17011a870044..bc269c1e0b1a 100644 --- a/arch/riscv/kernel/cpufeature.c +++ b/arch/riscv/kernel/cpufeature.c @@ -22,6 +22,9 @@ #include <asm/hwcap.h> unsigned long elf_hwcap __read_mostly; +#ifdef CONFIG_FPU +bool no_fpu __read_mostly; +#endif void riscv_fill_hwcap(void) { @@ -58,4 +61,12 @@ void riscv_fill_hwcap(void) elf_hwcap |= isa2hwcap[(unsigned char)(isa[i])]; pr_info("elf_hwcap is 0x%lx", elf_hwcap); + +#ifdef CONFIG_FPU + no_fpu = 0; + if (!(elf_hwcap & (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D))) { + pr_info("Bypass FPU code."); + no_fpu = 1; + } +#endif } diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c index 2450b824d799..9714e4fccb69 100644 --- a/arch/riscv/kernel/signal.c +++ b/arch/riscv/kernel/signal.c @@ -45,6 +45,9 @@ static long restore_fp_state(struct pt_regs *regs, struct __riscv_d_ext_state __user *state = &sc_fpregs->d; size_t i; + if (unlikely(no_fpu)) + return 0; + err = __copy_from_user(¤t->thread.fstate, state, sizeof(*state)); if (unlikely(err)) return err; @@ -72,6 +75,9 @@ static long save_fp_state(struct pt_regs *regs, struct __riscv_d_ext_state __user *state = &sc_fpregs->d; size_t i; + if (unlikely(no_fpu)) + return 0; + fstate_save(current, regs); err = __copy_to_user(state, ¤t->thread.fstate, sizeof(*state)); if (unlikely(err)) -- 2.18.0
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