[PATCH V4] LoongArch: Provide kernel fpu functions

[Huacai Chen]

Provide kernel_fpu_begin()/kernel_fpu_end() to allow the kernel itself
to use fpu. They can be used by some other kernel components, e.g., the
AMDGPU graphic driver for DCN.

Reported-by: WANG Xuerui <kernel@xxxxxxxxxx>
Tested-by: WANG Xuerui <kernel@xxxxxxxxxx>
Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
---
V2: Use non-GPL exports and update commit messages.
V3: Add spaces for coding style.
V4: WARN_ON unexpected requests and use GPL exports again.

 arch/loongarch/include/asm/fpu.h |  3 +++
 arch/loongarch/kernel/Makefile   |  2 +-
 arch/loongarch/kernel/kfpu.c     | 43 ++++++++++++++++++++++++++++++++
 3 files changed, 47 insertions(+), 1 deletion(-)
 create mode 100644 arch/loongarch/kernel/kfpu.c

diff --git a/arch/loongarch/include/asm/fpu.h b/arch/loongarch/include/asm/fpu.h
index 358b254d9c1d..192f8e35d912 100644
--- a/arch/loongarch/include/asm/fpu.h
+++ b/arch/loongarch/include/asm/fpu.h
@@ -21,6 +21,9 @@
 
 struct sigcontext;
 
+extern void kernel_fpu_begin(void);
+extern void kernel_fpu_end(void);
+
 extern void _init_fpu(unsigned int);
 extern void _save_fp(struct loongarch_fpu *);
 extern void _restore_fp(struct loongarch_fpu *);
diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
index 78d4e3384305..9a72d91cd104 100644
--- a/arch/loongarch/kernel/Makefile
+++ b/arch/loongarch/kernel/Makefile
@@ -13,7 +13,7 @@ obj-y		+= head.o cpu-probe.o cacheinfo.o env.o setup.o entry.o genex.o \
 obj-$(CONFIG_ACPI)		+= acpi.o
 obj-$(CONFIG_EFI) 		+= efi.o
 
-obj-$(CONFIG_CPU_HAS_FPU)	+= fpu.o
+obj-$(CONFIG_CPU_HAS_FPU)	+= fpu.o kfpu.o
 
 obj-$(CONFIG_ARCH_STRICT_ALIGN)	+= unaligned.o
 
diff --git a/arch/loongarch/kernel/kfpu.c b/arch/loongarch/kernel/kfpu.c
new file mode 100644
index 000000000000..aa68a1f6dec4
--- /dev/null
+++ b/arch/loongarch/kernel/kfpu.c
@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023 Loongson Technology Corporation Limited
+ */
+
+#include <linux/cpu.h>
+#include <linux/init.h>
+#include <asm/fpu.h>
+#include <asm/smp.h>
+
+static DEFINE_PER_CPU(bool, in_kernel_fpu);
+
+void kernel_fpu_begin(void)
+{
+	preempt_disable();
+
+	WARN_ON(this_cpu_read(in_kernel_fpu));
+
+	this_cpu_write(in_kernel_fpu, true);
+
+	if (!is_fpu_owner())
+		enable_fpu();
+	else
+		_save_fp(&current->thread.fpu);
+
+	write_fcsr(LOONGARCH_FCSR0, 0);
+}
+EXPORT_SYMBOL_GPL(kernel_fpu_begin);
+
+void kernel_fpu_end(void)
+{
+	WARN_ON(!this_cpu_read(in_kernel_fpu));
+
+	if (!is_fpu_owner())
+		disable_fpu();
+	else
+		_restore_fp(&current->thread.fpu);
+
+	this_cpu_write(in_kernel_fpu, false);
+
+	preempt_enable();
+}
+EXPORT_SYMBOL_GPL(kernel_fpu_end);
-- 
2.39.1