The patch titled
Subject: riscv: add support for kernel-mode FPU
has been added to the -mm mm-nonmm-unstable branch. Its filename is
riscv-add-support-for-kernel-mode-fpu.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/riscv-add-support-for-kernel-mode-fpu.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Samuel Holland <samuel.holland@xxxxxxxxxx>
Subject: riscv: add support for kernel-mode FPU
Date: Wed, 27 Mar 2024 13:00:41 -0700
This is motivated by the amdgpu DRM driver, which needs floating-point
code to support recent hardware. That code is not performance-critical,
so only provide a minimal non-preemptible implementation for now.
Support is limited to riscv64 because riscv32 requires runtime (libgcc)
assistance to convert between doubles and 64-bit integers.
Link: https://lkml.kernel.org/r/20240327200157.1097089-11-samuel.holland@xxxxxxxxxx
Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx>
Acked-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
Reviewed-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Cc: Alex Deucher <alexander.deucher@xxxxxxx>
Cc: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Huacai Chen <chenhuacai@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
Cc: Nicolas Schier <nicolas@xxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: WANG Xuerui <git@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/riscv/Kconfig | 1
arch/riscv/Makefile | 3 ++
arch/riscv/include/asm/fpu.h | 16 ++++++++++++++
arch/riscv/kernel/Makefile | 1
arch/riscv/kernel/kernel_mode_fpu.c | 28 ++++++++++++++++++++++++++
5 files changed, 49 insertions(+)
--- /dev/null
+++ a/arch/riscv/include/asm/fpu.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2023 SiFive
+ */
+
+#ifndef _ASM_RISCV_FPU_H
+#define _ASM_RISCV_FPU_H
+
+#include <asm/switch_to.h>
+
+#define kernel_fpu_available() has_fpu()
+
+void kernel_fpu_begin(void);
+void kernel_fpu_end(void);
+
+#endif /* ! _ASM_RISCV_FPU_H */
--- a/arch/riscv/Kconfig~riscv-add-support-for-kernel-mode-fpu
+++ a/arch/riscv/Kconfig
@@ -27,6 +27,7 @@ config RISCV
select ARCH_HAS_GCOV_PROFILE_ALL
select ARCH_HAS_GIGANTIC_PAGE
select ARCH_HAS_KCOV
+ select ARCH_HAS_KERNEL_FPU_SUPPORT if 64BIT && FPU
select ARCH_HAS_MEMBARRIER_CALLBACKS
select ARCH_HAS_MEMBARRIER_SYNC_CORE
select ARCH_HAS_MMIOWB
--- /dev/null
+++ a/arch/riscv/kernel/kernel_mode_fpu.c
@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023 SiFive
+ */
+
+#include <linux/export.h>
+#include <linux/preempt.h>
+
+#include <asm/csr.h>
+#include <asm/fpu.h>
+#include <asm/processor.h>
+#include <asm/switch_to.h>
+
+void kernel_fpu_begin(void)
+{
+ preempt_disable();
+ fstate_save(current, task_pt_regs(current));
+ csr_set(CSR_SSTATUS, SR_FS);
+}
+EXPORT_SYMBOL_GPL(kernel_fpu_begin);
+
+void kernel_fpu_end(void)
+{
+ csr_clear(CSR_SSTATUS, SR_FS);
+ fstate_restore(current, task_pt_regs(current));
+ preempt_enable();
+}
+EXPORT_SYMBOL_GPL(kernel_fpu_end);
--- a/arch/riscv/kernel/Makefile~riscv-add-support-for-kernel-mode-fpu
+++ a/arch/riscv/kernel/Makefile
@@ -67,6 +67,7 @@ obj-$(CONFIG_RISCV_MISALIGNED) += unalig
obj-$(CONFIG_RISCV_PROBE_UNALIGNED_ACCESS) += copy-unaligned.o
obj-$(CONFIG_FPU) += fpu.o
+obj-$(CONFIG_FPU) += kernel_mode_fpu.o
obj-$(CONFIG_RISCV_ISA_V) += vector.o
obj-$(CONFIG_RISCV_ISA_V) += kernel_mode_vector.o
obj-$(CONFIG_SMP) += smpboot.o
--- a/arch/riscv/Makefile~riscv-add-support-for-kernel-mode-fpu
+++ a/arch/riscv/Makefile
@@ -84,6 +84,9 @@ KBUILD_CFLAGS += -march=$(shell echo $(r
KBUILD_AFLAGS += -march=$(riscv-march-y)
+# For C code built with floating-point support, exclude V but keep F and D.
+CC_FLAGS_FPU := -march=$(shell echo $(riscv-march-y) | sed -E 's/(rv32ima|rv64ima)([^v_]*)v?/\1\2/')
+
KBUILD_CFLAGS += -mno-save-restore
KBUILD_CFLAGS += -DCONFIG_PAGE_OFFSET=$(CONFIG_PAGE_OFFSET)
_
Patches currently in -mm which might be from samuel.holland@xxxxxxxxxx are
arch-add-arch_has_kernel_fpu_support.patch
arm-implement-arch_has_kernel_fpu_support.patch
arm-crypto-use-cc_flags_fpu-for-neon-cflags.patch
arm64-implement-arch_has_kernel_fpu_support.patch
arm64-crypto-use-cc_flags_fpu-for-neon-cflags.patch
lib-raid6-use-cc_flags_fpu-for-neon-cflags.patch
loongarch-implement-arch_has_kernel_fpu_support.patch
powerpc-implement-arch_has_kernel_fpu_support.patch
x86-implement-arch_has_kernel_fpu_support.patch
riscv-add-support-for-kernel-mode-fpu.patch
drm-amd-display-use-arch_has_kernel_fpu_support.patch
selftests-fpu-move-fp-code-to-a-separate-translation-unit.patch
selftests-fpu-allow-building-on-other-architectures.patch
