2023-03-10 02:51:58

by Huacai Chen

Subject: [PATCH V4] LoongArch: Provide kernel fpu functions

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 <[email protected]>
Tested-by: WANG Xuerui <[email protected]>
Signed-off-by: Huacai Chen <[email protected]>
---
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

2023-03-10 06:33:31

by WANG Xuerui

Subject: Re: [PATCH V4] LoongArch: Provide kernel fpu functions

On 2023/3/10 10:51, Huacai Chen wrote:
> 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.

Actually, as Christoph suggested earlier, you should probably send this
together with the amdgpu modifications so that "actual usage" of the
interface is established.

>
> Reported-by: WANG Xuerui <[email protected]>
> Tested-by: WANG Xuerui <[email protected]>
> Signed-off-by: Huacai Chen <[email protected]>
> ---
> 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.

We should probably provide more archaeology or legal evidence as to why
the in-kernel FPU ops must be GPL-only. After all the status quo is that
among all arches that provide such ops, only the x86 ones are exported
GPL, so if loongarch should go GPL for this interface then probably
everyone else should too. It's not only affecting loongarch IMO.

>
> 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
>

--
WANG "xen0n" Xuerui

Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/

2023-03-10 08:33:57

by Xi Ruoyao

Subject: Re: [PATCH V4] LoongArch: Provide kernel fpu functions

On Fri, 2023-03-10 at 14:33 +0800, WANG Xuerui wrote:
> We should probably provide more archaeology or legal evidence as to why
> the in-kernel FPU ops must be GPL-only. After all the status quo is that
> among all arches that provide such ops, only the x86 ones are exported
> GPL, so if loongarch should go GPL for this interface then probably
> everyone else should too. It's not only affecting loongarch IMO.

If it's forced by GPL we should change the other arch's similar function
to EXPORT_GPL immediately.

--
Xi Ruoyao <[email protected]>
School of Aerospace Science and Technology, Xidian University