[PATCH v8 0/5] riscv: Add support to no-FPU systems

[PATCH v8 0/5] riscv: Add support to no-FPU systems

[Alan Kao]

This patchset adds an option, CONFIG_FPU, to enable/disable floating-
point procedures.

Kernel's new behavior will be as follows:

* with CONFIG_FPU=y
  All FPU codes are reserved.  If no FPU is found during booting, a
  global flag will be set, and those functions will be bypassed with
  condition check to that flag.

* with CONFIG_FPU=n
  No floating-point instructions in kernel and all related settings
  are excluded.

Changes in v8:
 - Fix a build fail introduced in v7.

Changes in v7:
 - Remove "fd" attribute from KBUILD_CFLAGS.

Changes in v6 (PATCH 0005 only):
 - Make the flag checking neater.

Changes in v5:
 - Invert the polarity of checking flag from no_fpu to has_fpu.

Changes in v4:
 - Append a new patch to detect existence of FPU and followups.
 - Add SPDX header to newly created fpu.S.
 - Fix a build error, sorry for that.
 - Fix wording, style, etc.

Changes in v3:
 - Refactor the whole patch into independent ones.

Changes in v2:
 - Various code cleanups and style fixes.

Alan Kao (5):
  Extract FPU context operations from entry.S
  Refactor FPU code in signal setup/return procedures
  Cleanup ISA string setting
  Allow to disable FPU support
  Auto-detect whether a FPU exists

 arch/riscv/Kconfig                 |   9 ++++
 arch/riscv/Makefile                |  19 +++----
 arch/riscv/include/asm/switch_to.h |  12 ++++-
 arch/riscv/kernel/Makefile         |   1 +
 arch/riscv/kernel/cpufeature.c     |   8 +++
 arch/riscv/kernel/entry.S          |  87 ------------------------------
 arch/riscv/kernel/fpu.S            | 106 +++++++++++++++++++++++++++++++++++++
 arch/riscv/kernel/process.c        |   6 ++-
 arch/riscv/kernel/signal.c         |  75 ++++++++++++++++----------
 9 files changed, 196 insertions(+), 127 deletions(-)
 create mode 100644 arch/riscv/kernel/fpu.S

-- 
2.7.4

[PATCH v8 1/5] Extract FPU context operations from entry.S

[Alan Kao]

We move __fstate_save and __fstate_restore to a new source
file, fpu.S.

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>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 arch/riscv/kernel/Makefile |   1 +
 arch/riscv/kernel/entry.S  |  87 -------------------------------------
 arch/riscv/kernel/fpu.S    | 106 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 107 insertions(+), 87 deletions(-)
 create mode 100644 arch/riscv/kernel/fpu.S

diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index e1274fc..bd433efd 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -13,6 +13,7 @@ extra-y += vmlinux.lds
 obj-y	+= cpu.o
 obj-y	+= cpufeature.o
 obj-y	+= entry.o
+obj-y	+= fpu.o
 obj-y	+= irq.o
 obj-y	+= process.o
 obj-y	+= ptrace.o
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index fa2c08e..59c02e2 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -357,93 +357,6 @@ ENTRY(__switch_to)
 	ret
 ENDPROC(__switch_to)
 
-ENTRY(__fstate_save)
-	li  a2,  TASK_THREAD_F0
-	add a0, a0, a2
-	li t1, SR_FS
-	csrs sstatus, t1
-	frcsr t0
-	fsd f0,  TASK_THREAD_F0_F0(a0)
-	fsd f1,  TASK_THREAD_F1_F0(a0)
-	fsd f2,  TASK_THREAD_F2_F0(a0)
-	fsd f3,  TASK_THREAD_F3_F0(a0)
-	fsd f4,  TASK_THREAD_F4_F0(a0)
-	fsd f5,  TASK_THREAD_F5_F0(a0)
-	fsd f6,  TASK_THREAD_F6_F0(a0)
-	fsd f7,  TASK_THREAD_F7_F0(a0)
-	fsd f8,  TASK_THREAD_F8_F0(a0)
-	fsd f9,  TASK_THREAD_F9_F0(a0)
-	fsd f10, TASK_THREAD_F10_F0(a0)
-	fsd f11, TASK_THREAD_F11_F0(a0)
-	fsd f12, TASK_THREAD_F12_F0(a0)
-	fsd f13, TASK_THREAD_F13_F0(a0)
-	fsd f14, TASK_THREAD_F14_F0(a0)
-	fsd f15, TASK_THREAD_F15_F0(a0)
-	fsd f16, TASK_THREAD_F16_F0(a0)
-	fsd f17, TASK_THREAD_F17_F0(a0)
-	fsd f18, TASK_THREAD_F18_F0(a0)
-	fsd f19, TASK_THREAD_F19_F0(a0)
-	fsd f20, TASK_THREAD_F20_F0(a0)
-	fsd f21, TASK_THREAD_F21_F0(a0)
-	fsd f22, TASK_THREAD_F22_F0(a0)
-	fsd f23, TASK_THREAD_F23_F0(a0)
-	fsd f24, TASK_THREAD_F24_F0(a0)
-	fsd f25, TASK_THREAD_F25_F0(a0)
-	fsd f26, TASK_THREAD_F26_F0(a0)
-	fsd f27, TASK_THREAD_F27_F0(a0)
-	fsd f28, TASK_THREAD_F28_F0(a0)
-	fsd f29, TASK_THREAD_F29_F0(a0)
-	fsd f30, TASK_THREAD_F30_F0(a0)
-	fsd f31, TASK_THREAD_F31_F0(a0)
-	sw t0, TASK_THREAD_FCSR_F0(a0)
-	csrc sstatus, t1
-	ret
-ENDPROC(__fstate_save)
-
-ENTRY(__fstate_restore)
-	li  a2,  TASK_THREAD_F0
-	add a0, a0, a2
-	li t1, SR_FS
-	lw t0, TASK_THREAD_FCSR_F0(a0)
-	csrs sstatus, t1
-	fld f0,  TASK_THREAD_F0_F0(a0)
-	fld f1,  TASK_THREAD_F1_F0(a0)
-	fld f2,  TASK_THREAD_F2_F0(a0)
-	fld f3,  TASK_THREAD_F3_F0(a0)
-	fld f4,  TASK_THREAD_F4_F0(a0)
-	fld f5,  TASK_THREAD_F5_F0(a0)
-	fld f6,  TASK_THREAD_F6_F0(a0)
-	fld f7,  TASK_THREAD_F7_F0(a0)
-	fld f8,  TASK_THREAD_F8_F0(a0)
-	fld f9,  TASK_THREAD_F9_F0(a0)
-	fld f10, TASK_THREAD_F10_F0(a0)
-	fld f11, TASK_THREAD_F11_F0(a0)
-	fld f12, TASK_THREAD_F12_F0(a0)
-	fld f13, TASK_THREAD_F13_F0(a0)
-	fld f14, TASK_THREAD_F14_F0(a0)
-	fld f15, TASK_THREAD_F15_F0(a0)
-	fld f16, TASK_THREAD_F16_F0(a0)
-	fld f17, TASK_THREAD_F17_F0(a0)
-	fld f18, TASK_THREAD_F18_F0(a0)
-	fld f19, TASK_THREAD_F19_F0(a0)
-	fld f20, TASK_THREAD_F20_F0(a0)
-	fld f21, TASK_THREAD_F21_F0(a0)
-	fld f22, TASK_THREAD_F22_F0(a0)
-	fld f23, TASK_THREAD_F23_F0(a0)
-	fld f24, TASK_THREAD_F24_F0(a0)
-	fld f25, TASK_THREAD_F25_F0(a0)
-	fld f26, TASK_THREAD_F26_F0(a0)
-	fld f27, TASK_THREAD_F27_F0(a0)
-	fld f28, TASK_THREAD_F28_F0(a0)
-	fld f29, TASK_THREAD_F29_F0(a0)
-	fld f30, TASK_THREAD_F30_F0(a0)
-	fld f31, TASK_THREAD_F31_F0(a0)
-	fscsr t0
-	csrc sstatus, t1
-	ret
-ENDPROC(__fstate_restore)
-
-
 	.section ".rodata"
 	/* Exception vector table */
 ENTRY(excp_vect_table)
diff --git a/arch/riscv/kernel/fpu.S b/arch/riscv/kernel/fpu.S
new file mode 100644
index 0000000..1defb06
--- /dev/null
+++ b/arch/riscv/kernel/fpu.S
@@ -0,0 +1,106 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2012 Regents of the University of California
+ * Copyright (C) 2017 SiFive
+ *
+ *   This program is free software; you can redistribute it and/or
+ *   modify it under the terms of the GNU General Public License
+ *   as published by the Free Software Foundation, version 2.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ */
+
+#include <linux/linkage.h>
+
+#include <asm/asm.h>
+#include <asm/csr.h>
+#include <asm/asm-offsets.h>
+
+ENTRY(__fstate_save)
+	li  a2,  TASK_THREAD_F0
+	add a0, a0, a2
+	li t1, SR_FS
+	csrs sstatus, t1
+	frcsr t0
+	fsd f0,  TASK_THREAD_F0_F0(a0)
+	fsd f1,  TASK_THREAD_F1_F0(a0)
+	fsd f2,  TASK_THREAD_F2_F0(a0)
+	fsd f3,  TASK_THREAD_F3_F0(a0)
+	fsd f4,  TASK_THREAD_F4_F0(a0)
+	fsd f5,  TASK_THREAD_F5_F0(a0)
+	fsd f6,  TASK_THREAD_F6_F0(a0)
+	fsd f7,  TASK_THREAD_F7_F0(a0)
+	fsd f8,  TASK_THREAD_F8_F0(a0)
+	fsd f9,  TASK_THREAD_F9_F0(a0)
+	fsd f10, TASK_THREAD_F10_F0(a0)
+	fsd f11, TASK_THREAD_F11_F0(a0)
+	fsd f12, TASK_THREAD_F12_F0(a0)
+	fsd f13, TASK_THREAD_F13_F0(a0)
+	fsd f14, TASK_THREAD_F14_F0(a0)
+	fsd f15, TASK_THREAD_F15_F0(a0)
+	fsd f16, TASK_THREAD_F16_F0(a0)
+	fsd f17, TASK_THREAD_F17_F0(a0)
+	fsd f18, TASK_THREAD_F18_F0(a0)
+	fsd f19, TASK_THREAD_F19_F0(a0)
+	fsd f20, TASK_THREAD_F20_F0(a0)
+	fsd f21, TASK_THREAD_F21_F0(a0)
+	fsd f22, TASK_THREAD_F22_F0(a0)
+	fsd f23, TASK_THREAD_F23_F0(a0)
+	fsd f24, TASK_THREAD_F24_F0(a0)
+	fsd f25, TASK_THREAD_F25_F0(a0)
+	fsd f26, TASK_THREAD_F26_F0(a0)
+	fsd f27, TASK_THREAD_F27_F0(a0)
+	fsd f28, TASK_THREAD_F28_F0(a0)
+	fsd f29, TASK_THREAD_F29_F0(a0)
+	fsd f30, TASK_THREAD_F30_F0(a0)
+	fsd f31, TASK_THREAD_F31_F0(a0)
+	sw t0, TASK_THREAD_FCSR_F0(a0)
+	csrc sstatus, t1
+	ret
+ENDPROC(__fstate_save)
+
+ENTRY(__fstate_restore)
+	li  a2,  TASK_THREAD_F0
+	add a0, a0, a2
+	li t1, SR_FS
+	lw t0, TASK_THREAD_FCSR_F0(a0)
+	csrs sstatus, t1
+	fld f0,  TASK_THREAD_F0_F0(a0)
+	fld f1,  TASK_THREAD_F1_F0(a0)
+	fld f2,  TASK_THREAD_F2_F0(a0)
+	fld f3,  TASK_THREAD_F3_F0(a0)
+	fld f4,  TASK_THREAD_F4_F0(a0)
+	fld f5,  TASK_THREAD_F5_F0(a0)
+	fld f6,  TASK_THREAD_F6_F0(a0)
+	fld f7,  TASK_THREAD_F7_F0(a0)
+	fld f8,  TASK_THREAD_F8_F0(a0)
+	fld f9,  TASK_THREAD_F9_F0(a0)
+	fld f10, TASK_THREAD_F10_F0(a0)
+	fld f11, TASK_THREAD_F11_F0(a0)
+	fld f12, TASK_THREAD_F12_F0(a0)
+	fld f13, TASK_THREAD_F13_F0(a0)
+	fld f14, TASK_THREAD_F14_F0(a0)
+	fld f15, TASK_THREAD_F15_F0(a0)
+	fld f16, TASK_THREAD_F16_F0(a0)
+	fld f17, TASK_THREAD_F17_F0(a0)
+	fld f18, TASK_THREAD_F18_F0(a0)
+	fld f19, TASK_THREAD_F19_F0(a0)
+	fld f20, TASK_THREAD_F20_F0(a0)
+	fld f21, TASK_THREAD_F21_F0(a0)
+	fld f22, TASK_THREAD_F22_F0(a0)
+	fld f23, TASK_THREAD_F23_F0(a0)
+	fld f24, TASK_THREAD_F24_F0(a0)
+	fld f25, TASK_THREAD_F25_F0(a0)
+	fld f26, TASK_THREAD_F26_F0(a0)
+	fld f27, TASK_THREAD_F27_F0(a0)
+	fld f28, TASK_THREAD_F28_F0(a0)
+	fld f29, TASK_THREAD_F29_F0(a0)
+	fld f30, TASK_THREAD_F30_F0(a0)
+	fld f31, TASK_THREAD_F31_F0(a0)
+	fscsr t0
+	csrc sstatus, t1
+	ret
+ENDPROC(__fstate_restore)
-- 
2.7.4

[PATCH v8 2/5] Refactor FPU code in signal setup/return procedures

[Alan Kao]

FPU-related logic is separated from normal signal handling path in
this patch.  Kernel can easily be configured to exclude those procedures
for no-FPU systems.

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>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 arch/riscv/kernel/signal.c | 68 ++++++++++++++++++++++++++++------------------
 1 file changed, 41 insertions(+), 27 deletions(-)

diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
index 718d0c9..6a18b98 100644
--- a/arch/riscv/kernel/signal.c
+++ b/arch/riscv/kernel/signal.c
@@ -37,45 +37,63 @@ struct rt_sigframe {
 	struct ucontext uc;
 };
 
-static long restore_d_state(struct pt_regs *regs,
-	struct __riscv_d_ext_state __user *state)
+static long restore_fp_state(struct pt_regs *regs,
+			     union __riscv_fp_state *sc_fpregs)
 {
 	long err;
+	struct __riscv_d_ext_state __user *state = &sc_fpregs->d;
+	size_t i;
+
 	err = __copy_from_user(&current->thread.fstate, state, sizeof(*state));
-	if (likely(!err))
-		fstate_restore(current, regs);
+	if (unlikely(err))
+		return err;
+
+	fstate_restore(current, regs);
+
+	/* We support no other extension state at this time. */
+	for (i = 0; i < ARRAY_SIZE(sc_fpregs->q.reserved); i++) {
+		u32 value;
+
+		err = __get_user(value, &sc_fpregs->q.reserved[i]);
+		if (unlikely(err))
+			break;
+		if (value != 0)
+			return -EINVAL;
+	}
+
 	return err;
 }
 
-static long save_d_state(struct pt_regs *regs,
-	struct __riscv_d_ext_state __user *state)
+static long save_fp_state(struct pt_regs *regs,
+			  union __riscv_fp_state *sc_fpregs)
 {
+	long err;
+	struct __riscv_d_ext_state __user *state = &sc_fpregs->d;
+	size_t i;
+
 	fstate_save(current, regs);
-	return __copy_to_user(state, &current->thread.fstate, sizeof(*state));
+	err = __copy_to_user(state, &current->thread.fstate, sizeof(*state));
+	if (unlikely(err))
+		return err;
+
+	/* We support no other extension state at this time. */
+	for (i = 0; i < ARRAY_SIZE(sc_fpregs->q.reserved); i++) {
+		err = __put_user(0, &sc_fpregs->q.reserved[i]);
+		if (unlikely(err))
+			break;
+	}
+
+	return err;
 }
 
 static long restore_sigcontext(struct pt_regs *regs,
 	struct sigcontext __user *sc)
 {
 	long err;
-	size_t i;
 	/* sc_regs is structured the same as the start of pt_regs */
 	err = __copy_from_user(regs, &sc->sc_regs, sizeof(sc->sc_regs));
-	if (unlikely(err))
-		return err;
 	/* Restore the floating-point state. */
-	err = restore_d_state(regs, &sc->sc_fpregs.d);
-	if (unlikely(err))
-		return err;
-	/* We support no other extension state at this time. */
-	for (i = 0; i < ARRAY_SIZE(sc->sc_fpregs.q.reserved); i++) {
-		u32 value;
-		err = __get_user(value, &sc->sc_fpregs.q.reserved[i]);
-		if (unlikely(err))
-			break;
-		if (value != 0)
-			return -EINVAL;
-	}
+	err |= restore_fp_state(regs, &sc->sc_fpregs);
 	return err;
 }
 
@@ -124,14 +142,10 @@ static long setup_sigcontext(struct rt_sigframe __user *frame,
 {
 	struct sigcontext __user *sc = &frame->uc.uc_mcontext;
 	long err;
-	size_t i;
 	/* 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_d_state(regs, &sc->sc_fpregs.d);
-	/* We support no other extension state at this time. */
-	for (i = 0; i < ARRAY_SIZE(sc->sc_fpregs.q.reserved); i++)
-		err |= __put_user(0, &sc->sc_fpregs.q.reserved[i]);
+	err |= save_fp_state(regs, &sc->sc_fpregs);
 	return err;
 }
 
-- 
2.7.4

[PATCH v8 3/5] Cleanup ISA string setting

[Alan Kao]

This patch cleanup the MARCH string passing to both compiler and
assembler.  Note that the CFLAGS should not contain "fd" before we
have mechnisms like kernel_fpu_begin/end in other architectures.

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/Makefile | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 61ec424..01393e1 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -28,7 +28,6 @@ ifeq ($(CONFIG_ARCH_RV64I),y)
 	
 	KBUILD_CFLAGS	+= $(call cc-ifversion, -ge, 0500, -DCONFIG_ARCH_SUPPORTS_INT128)
 
-	KBUILD_MARCH = rv64im
 	KBUILD_LDFLAGS += -melf64lriscv
 else
 	BITS := 32
@@ -36,22 +35,20 @@ else
 
 	KBUILD_CFLAGS += -mabi=ilp32
 	KBUILD_AFLAGS += -mabi=ilp32
-	KBUILD_MARCH = rv32im
 	KBUILD_LDFLAGS += -melf32lriscv
 endif
 
 KBUILD_CFLAGS += -Wall
 
-ifeq ($(CONFIG_RISCV_ISA_A),y)
-	KBUILD_ARCH_A = a
-endif
-ifeq ($(CONFIG_RISCV_ISA_C),y)
-	KBUILD_ARCH_C = c
-endif
-
-KBUILD_AFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)fd$(KBUILD_ARCH_C)
+# ISA string setting
+riscv-march-$(CONFIG_ARCH_RV32I)	:= rv32im
+riscv-march-$(CONFIG_ARCH_RV64I)	:= rv64im
+riscv-march-$(CONFIG_RISCV_ISA_A)	:= $(riscv-march-y)a
+riscv-march-y				:= $(riscv-march-y)fd
+riscv-march-$(CONFIG_RISCV_ISA_C)	:= $(riscv-march-y)c
+KBUILD_CFLAGS += -march=$(subst fd,,$(riscv-march-y))
+KBUILD_AFLAGS += -march=$(riscv-march-y)
 
-KBUILD_CFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)$(KBUILD_ARCH_C)
 KBUILD_CFLAGS += -mno-save-restore
 KBUILD_CFLAGS += -DCONFIG_PAGE_OFFSET=$(CONFIG_PAGE_OFFSET)
 
-- 
2.7.4

[PATCH v8 4/5] Allow to disable FPU support

[Alan Kao]

FPU codes have been separated from common part in previous patches.
This patch add the CONFIG_FPU option and some stubs, so that a no-FPU
configuration is allowed.

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>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 arch/riscv/Kconfig                 |  9 +++++++++
 arch/riscv/Makefile                |  2 +-
 arch/riscv/include/asm/switch_to.h | 10 ++++++++++
 arch/riscv/kernel/Makefile         |  2 +-
 arch/riscv/kernel/process.c        |  4 +++-
 arch/riscv/kernel/signal.c         |  5 +++++
 6 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index a344980..a63f9db 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -208,6 +208,15 @@ config RISCV_BASE_PMU
 
 endmenu
 
+config FPU
+	bool "FPU support"
+	default y
+	help
+	  Say N here if you want to disable all floating-point related procedure
+	  in the kernel.
+
+	  If you don't know what to do here, say Y.
+
 endmenu
 
 menu "Kernel type"
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 01393e1..901770f 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -44,7 +44,7 @@ KBUILD_CFLAGS += -Wall
 riscv-march-$(CONFIG_ARCH_RV32I)	:= rv32im
 riscv-march-$(CONFIG_ARCH_RV64I)	:= rv64im
 riscv-march-$(CONFIG_RISCV_ISA_A)	:= $(riscv-march-y)a
-riscv-march-y				:= $(riscv-march-y)fd
+riscv-march-$(CONFIG_FPU)		:= $(riscv-march-y)fd
 riscv-march-$(CONFIG_RISCV_ISA_C)	:= $(riscv-march-y)c
 KBUILD_CFLAGS += -march=$(subst fd,,$(riscv-march-y))
 KBUILD_AFLAGS += -march=$(riscv-march-y)
diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
index dd6b05b..093050b 100644
--- a/arch/riscv/include/asm/switch_to.h
+++ b/arch/riscv/include/asm/switch_to.h
@@ -18,6 +18,7 @@
 #include <asm/ptrace.h>
 #include <asm/csr.h>
 
+#ifdef CONFIG_FPU
 extern void __fstate_save(struct task_struct *save_to);
 extern void __fstate_restore(struct task_struct *restore_from);
 
@@ -55,6 +56,15 @@ 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)
+
+#else
+#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 *,
 				       struct task_struct *);
 
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index bd433efd..f13f7f2 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -13,7 +13,6 @@ extra-y += vmlinux.lds
 obj-y	+= cpu.o
 obj-y	+= cpufeature.o
 obj-y	+= entry.o
-obj-y	+= fpu.o
 obj-y	+= irq.o
 obj-y	+= process.o
 obj-y	+= ptrace.o
@@ -32,6 +31,7 @@ obj-y	+= vdso/
 
 CFLAGS_setup.o := -mcmodel=medany
 
+obj-$(CONFIG_FPU)		+= fpu.o
 obj-$(CONFIG_SMP)		+= smpboot.o
 obj-$(CONFIG_SMP)		+= smp.o
 obj-$(CONFIG_MODULES)		+= module.o
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index d7c6ca7..07d5156 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -76,7 +76,7 @@ void show_regs(struct pt_regs *regs)
 void start_thread(struct pt_regs *regs, unsigned long pc,
 	unsigned long sp)
 {
-	regs->sstatus = SR_SPIE /* User mode, irqs on */ | SR_FS_INITIAL;
+	regs->sstatus = DEFAULT_SSTATUS;
 	regs->sepc = pc;
 	regs->sp = sp;
 	set_fs(USER_DS);
@@ -84,12 +84,14 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
 
 void flush_thread(void)
 {
+#ifdef CONFIG_FPU
 	/*
 	 * Reset FPU context
 	 *	frm: round to nearest, ties to even (IEEE default)
 	 *	fflags: accrued exceptions cleared
 	 */
 	memset(&current->thread.fstate, 0, sizeof(current->thread.fstate));
+#endif
 }
 
 int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
index 6a18b98..2450b82 100644
--- a/arch/riscv/kernel/signal.c
+++ b/arch/riscv/kernel/signal.c
@@ -37,6 +37,7 @@ struct rt_sigframe {
 	struct ucontext uc;
 };
 
+#ifdef CONFIG_FPU
 static long restore_fp_state(struct pt_regs *regs,
 			     union __riscv_fp_state *sc_fpregs)
 {
@@ -85,6 +86,10 @@ static long save_fp_state(struct pt_regs *regs,
 
 	return err;
 }
+#else
+#define save_fp_state(task, regs) (0)
+#define restore_fp_state(task, regs) (0)
+#endif
 
 static long restore_sigcontext(struct pt_regs *regs,
 	struct sigcontext __user *sc)
-- 
2.7.4

[PATCH v8 5/5] Auto-detect whether a FPU exists

[Alan Kao]

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 093050b..7335590 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 17011a8..46942e6 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 07d5156..bef1999 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 2450b82..f9b5e7e 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;
 }
 
-- 
2.7.4

Re: [PATCH v8 3/5] Cleanup ISA string setting

[Guenter Roeck]

Hi,

On Tue, Oct 09, 2018 at 10:18:32AM +0800, Alan Kao wrote:
> This patch cleanup the MARCH string passing to both compiler and
> assembler.  Note that the CFLAGS should not contain "fd" before we
> have mechnisms like kernel_fpu_begin/end in other architectures.
> 
> 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>
> ---

With this patch in -next applied, I get the following error
when building riscv:defconfig.

cc1: error: -march=c: ISA string must begin with rv32 or rv64
cc1: error: ABI requires -march=rv64
Kbuild:21: recipe for target 'kernel/bounds.s' failed

This is seen with both gcc 7.3.0 and gcc 8.2.0. Bisect log is attached.

What am I missing ? Does RISC-V now require a new non-upstream compiler ?
Or a special version of make ? I am currently using GNU Make 4.1.

Thanks,
Guenter

---
# bad: [774ea0551a2966c8fc29a6f675c3e28c5c6fa586] Add linux-next specific files for 20181012
# good: [0238df646e6224016a45505d2c111a24669ebe21] Linux 4.19-rc7
git bisect start 'HEAD' 'v4.19-rc7'
# bad: [dfbf78faefa3c26d94208398e62bf25ea798e7f2] Merge remote-tracking branch 'spi-nor/spi-nor/next'
git bisect bad dfbf78faefa3c26d94208398e62bf25ea798e7f2
# bad: [530d65b38df62760ce7f778907cc3fce6f5519b7] Merge remote-tracking branch 'hid/for-next'
git bisect bad 530d65b38df62760ce7f778907cc3fce6f5519b7
# good: [4967343a2e8ae0ee767471053f8b55e529b7be7e] Merge remote-tracking branch 'arm-soc/for-next'
git bisect good 4967343a2e8ae0ee767471053f8b55e529b7be7e
# bad: [e8af1ded2dc3e3cb4e8c414809b2303f5b91abe0] Merge remote-tracking branch 'befs/for-next'
git bisect bad e8af1ded2dc3e3cb4e8c414809b2303f5b91abe0
# good: [1ccf1a61dd05b37ddc41fb874109915efb56c53d] Merge remote-tracking branch 'clk-samsung/for-next'
git bisect good 1ccf1a61dd05b37ddc41fb874109915efb56c53d
# good: [43693e88f9764f7ff292e18cbb0d36ed9b26411e] Merge remote-tracking branch 'powerpc/next'
git bisect good 43693e88f9764f7ff292e18cbb0d36ed9b26411e
# good: [52a34b34d4ff9a61bc6da9740541d8f08a40438c] s390/crypto: Enhance paes cipher to accept variable length key material
git bisect good 52a34b34d4ff9a61bc6da9740541d8f08a40438c
# bad: [cc932c65d7892091735a553b89fdd21cc20cb85d] Merge remote-tracking branch 's390/features'
git bisect bad cc932c65d7892091735a553b89fdd21cc20cb85d
# bad: [bb0133e085b524a49829fd02be21f1edd3beaac1] automerging branch "kernel.org-palmer-linux/next-nofpu" into "for-next"
git bisect bad bb0133e085b524a49829fd02be21f1edd3beaac1
# good: [c720a7ff190fc2015ae1449bcbf31216c4a9e973] automerging branch "kernel.org-palmer-linux/next-hch" into "for-next"
git bisect good c720a7ff190fc2015ae1449bcbf31216c4a9e973
# bad: [27625655dbfd83205ba489183f45a87717cb867c] RISC-V: Auto-detect whether a FPU exists
git bisect bad 27625655dbfd83205ba489183f45a87717cb867c
# good: [5453696cb3f1e5b316511234e27570d2f7698b70] RISC-V: Refactor FPU code in signal setup/return procedures
git bisect good 5453696cb3f1e5b316511234e27570d2f7698b70
# bad: [919ecff9aac4e7c8dae05d924385fb05c7c63854] RISC-V: Allow to disable FPU support
git bisect bad 919ecff9aac4e7c8dae05d924385fb05c7c63854
# bad: [0a5bee05fc67ce2044b8d91a18abbf14042da531] RISC-V: Cleanup ISA string setting
git bisect bad 0a5bee05fc67ce2044b8d91a18abbf14042da531
# first bad commit: [0a5bee05fc67ce2044b8d91a18abbf14042da531] RISC-V: Cleanup ISA string setting

Re: [PATCH v8 3/5] Cleanup ISA string setting

[Alan Kao]

Hi Guenter,

On Sat, Oct 13, 2018 at 05:02:05PM -0700, Guenter Roeck wrote:
> Hi,
> 
> With this patch in -next applied, I get the following error
> when building riscv:defconfig.

I guess what you meant was this commit:
commit 0a5bee05fc67ce2044b8d91a18abbf14042da531

The modification in Makefile was

-endif
-
-KBUILD_AFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)fd$(KBUILD_ARCH_C)
+# ISA string setting
+riscv-march-$(CONFIG_ARCH_RV32I)       := rv32im
+riscv-march-$(CONFIG_ARCH_RV64I)       := rv64im
+riscv-march-$(CONFIG_RISCV_ISA_A)      := $(riscv-march-y)a
+riscv-march-y                          := fd
+riscv-march-$(CONFIG_RISCV_ISA_C)      := $(riscv-march-y)c

and the ":= fd" line was wrong.  It should have been 

+riscv-march-y                          := $(riscv-march-y)fd

> 
> 
> What am I missing ? Does RISC-V now require a new non-upstream compiler ?
> Or a special version of make ? I am currently using GNU Make 4.1.

So I sent the v8 to fix this problem.
Sorry for the inconvinience.

> 
> Thanks,
> Guenter
> 
> ---

And Palmer, it seems that the patch that causes this build error has been
pulled into linux-next.  Any idea how to fix that one?

Many thanks,
Alan

Re: [PATCH v8 3/5] Cleanup ISA string setting

[Guenter Roeck]

Hi Alan,

On 10/14/2018 04:46 PM, Alan Kao wrote:
> Hi Guenter,
> 
> On Sat, Oct 13, 2018 at 05:02:05PM -0700, Guenter Roeck wrote:
>> Hi,
>>
>> With this patch in -next applied, I get the following error
>> when building riscv:defconfig.
> 
> I guess what you meant was this commit:
> commit 0a5bee05fc67ce2044b8d91a18abbf14042da531
> 

Yes, sorry, I just blindly assumed that the last version I found must have caused
the problem. You are right, v8 actually fixes it (as suggested below).

> The modification in Makefile was
> 
> -endif
> -
> -KBUILD_AFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)fd$(KBUILD_ARCH_C)
> +# ISA string setting
> +riscv-march-$(CONFIG_ARCH_RV32I)       := rv32im
> +riscv-march-$(CONFIG_ARCH_RV64I)       := rv64im
> +riscv-march-$(CONFIG_RISCV_ISA_A)      := $(riscv-march-y)aj
> +riscv-march-y                          := fd
> +riscv-march-$(CONFIG_RISCV_ISA_C)      := $(riscv-march-y)c
> 
> and the ":= fd" line was wrong.  It should have been
> 
> +riscv-march-y                          := $(riscv-march-y)fd
> 
>>
>>
>> What am I missing ? Does RISC-V now require a new non-upstream compiler ?
>> Or a special version of make ? I am currently using GNU Make 4.1.
> 
> So I sent the v8 to fix this problem.
> Sorry for the inconvinience.
> 

No worries. At least this problem was (is going to be) easy to fix.
And, yes, I confirmed that the one-line change above fixes the problem.

Guenter

>>
>> Thanks,
>> Guenter
>>
>> ---
> 
> And Palmer, it seems that the patch that causes this build error has been
> pulled into linux-next.  Any idea how to fix that one?
> 
> Many thanks,
> Alan
> 

Re: [PATCH v8 3/5] Cleanup ISA string setting

[Palmer Dabbelt]

On Sun, 14 Oct 2018 16:46:40 PDT (-0700), alankao@andestech.com wrote:
> Hi Guenter,
>
> On Sat, Oct 13, 2018 at 05:02:05PM -0700, Guenter Roeck wrote:
>> Hi,
>>
>> With this patch in -next applied, I get the following error
>> when building riscv:defconfig.
>
> I guess what you meant was this commit:
> commit 0a5bee05fc67ce2044b8d91a18abbf14042da531
>
> The modification in Makefile was
>
> -endif
> -
> -KBUILD_AFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)fd$(KBUILD_ARCH_C)
> +# ISA string setting
> +riscv-march-$(CONFIG_ARCH_RV32I)       := rv32im
> +riscv-march-$(CONFIG_ARCH_RV64I)       := rv64im
> +riscv-march-$(CONFIG_RISCV_ISA_A)      := $(riscv-march-y)a
> +riscv-march-y                          := fd
> +riscv-march-$(CONFIG_RISCV_ISA_C)      := $(riscv-march-y)c
>
> and the ":= fd" line was wrong.  It should have been
>
> +riscv-march-y                          := $(riscv-march-y)fd
>
>>
>>
>> What am I missing ? Does RISC-V now require a new non-upstream compiler ?
>> Or a special version of make ? I am currently using GNU Make 4.1.
>
> So I sent the v8 to fix this problem.
> Sorry for the inconvinience.
>
>>
>> Thanks,
>> Guenter
>>
>> ---
>
> And Palmer, it seems that the patch that causes this build error has been
> pulled into linux-next.  Any idea how to fix that one?

If I run into the new version then I'll overwrite in in my for-next branch.  I 
don't see one, though...

Re: [PATCH v8 3/5] Cleanup ISA string setting

[Guenter Roeck]

On 10/15/2018 03:34 PM, Palmer Dabbelt wrote:
> On Sun, 14 Oct 2018 16:46:40 PDT (-0700), alankao@andestech.com wrote:
>> Hi Guenter,
>>
>> On Sat, Oct 13, 2018 at 05:02:05PM -0700, Guenter Roeck wrote:
>>> Hi,
>>>
>>> With this patch in -next applied, I get the following error
>>> when building riscv:defconfig.
>>
>> I guess what you meant was this commit:
>> commit 0a5bee05fc67ce2044b8d91a18abbf14042da531
>>
>> The modification in Makefile was
>>
>> -endif
>> -
>> -KBUILD_AFLAGS += -march=$(KBUILD_MARCH)$(KBUILD_ARCH_A)fd$(KBUILD_ARCH_C)
>> +# ISA string setting
>> +riscv-march-$(CONFIG_ARCH_RV32I)       := rv32im
>> +riscv-march-$(CONFIG_ARCH_RV64I)       := rv64im
>> +riscv-march-$(CONFIG_RISCV_ISA_A)      := $(riscv-march-y)a
>> +riscv-march-y                          := fd
>> +riscv-march-$(CONFIG_RISCV_ISA_C)      := $(riscv-march-y)c
>>
>> and the ":= fd" line was wrong.  It should have been
>>
>> +riscv-march-y                          := $(riscv-march-y)fd
>>
>>>
>>>
>>> What am I missing ? Does RISC-V now require a new non-upstream compiler ?
>>> Or a special version of make ? I am currently using GNU Make 4.1.
>>
>> So I sent the v8 to fix this problem.
>> Sorry for the inconvinience.
>>
>>>
>>> Thanks,
>>> Guenter
>>>
>>> ---
>>
>> And Palmer, it seems that the patch that causes this build error has been
>> pulled into linux-next.  Any idea how to fix that one?
> 
> If I run into the new version then I'll overwrite in in my for-next branch.  I don't see one, though...
> 

The series is on lore, lkml, and patchwork. Patchwork link to v8 of this patch:

https://lore.kernel.org/patchwork/patch/997407/

Guenter