From: Alan Kao <alankao@andestech.com>
To: <linux-kernel@vger.kernel.org>, <linux-riscv@lists.infradead.org>,
"Palmer Dabbelt" <palmer@sifive.com>,
Albert Ou <albert@sifive.com>,
Christoph Hellwig <hch@infradead.org>,
Andrew Waterman <andrew@sifive.com>,
Arnd Bergmann <arnd@arndb.de>, Darius Rad <darius@bluespec.com>
Cc: <greentime@andestech.com>, <vincentc@andestech.com>,
<zong@andestech.com>, <nickhu@andestech.com>,
Alan Kao <alankao@andestech.com>
Subject: [PATCH 5/5] Auto-detect whether a FPU exists
Date: Mon, 27 Aug 2018 09:07:55 +0800 [thread overview]
Message-ID: <1535332075-5727-6-git-send-email-alankao@andestech.com> (raw)
In-Reply-To: <1535332075-5727-1-git-send-email-alankao@andestech.com>
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>
---
arch/riscv/include/asm/switch_to.h | 8 ++++----
arch/riscv/kernel/cpufeature.c | 8 ++++++++
arch/riscv/kernel/process.c | 4 +++-
arch/riscv/kernel/signal.c | 6 ++++--
4 files changed, 19 insertions(+), 7 deletions(-)
diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
index 093050b03543..733559083f24 100644
--- a/arch/riscv/include/asm/switch_to.h
+++ b/arch/riscv/include/asm/switch_to.h
@@ -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)
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 17011a870044..46942e635266 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 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
}
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index 07d515655aa9..bef19993ea92 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -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);
diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
index 2450b824d799..f9b5e7e352ef 100644
--- a/arch/riscv/kernel/signal.c
+++ b/arch/riscv/kernel/signal.c
@@ -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;
}
--
2.18.0
next prev parent reply other threads:[~2018-08-27 1:08 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-27 1:07 [PATCH v7 0/5] riscv: Add support to no-FPU systems Alan Kao
2018-08-27 1:07 ` [PATCH 1/5] Extract FPU context operations from entry.S Alan Kao
2018-08-27 1:07 ` [PATCH 2/5] Refactor FPU code in signal setup/return procedures Alan Kao
2018-08-27 1:07 ` [PATCH 3/5] Cleanup ISA string setting Alan Kao
2018-08-30 14:31 ` Christoph Hellwig
2018-08-27 1:07 ` [PATCH 4/5] Allow to disable FPU support Alan Kao
2018-08-27 1:07 ` Alan Kao [this message]
2018-08-30 14:32 ` [PATCH 5/5] Auto-detect whether a FPU exists Christoph Hellwig
2018-09-06 9:45 ` [PATCH v7 0/5] riscv: Add support to no-FPU systems Palmer Dabbelt
2018-10-04 5:30 ` Alan Kao
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