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lib: sbi: Add floating-point context save/restore support.

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Add support for saving and restoring RISC-V floating-point (F/D) extension
state in OpenSBI. This introduces a floating-point context structure and
helper routines to perform full context save and restore.

The floating-point context includes storage for all 32 FPi registers (f0–f31)
along with the fcsr control and status register. The register state is saved
and restored using double-precision load/store instructions (fsd/fld), and
single-precision load/store instructions (fsw/flw) on an RV64 system with
F and D-extension support.

The implementation follows an eager context switching model where the entire
FP state is saved and restored on every context switch. This avoids the need
for trap-based lazy management and keeps the design simple and deterministic.

Signed-off-by: Dave Patel <dave.patel@riscstar.com>
Signed-off-by: Anup Patel <anup.patel@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260518083023.997323-3-anup.patel@oss.qualcomm.com
Signed-off-by: Anup Patel <anup@brainfault.org>
This commit is contained in:
Dave Patel
2026-05-18 14:00:22 +05:30
committed by Anup Patel
parent 21461156da
commit 718e1d194f
3 changed files with 228 additions and 0 deletions
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lib/sbi/sbi_fp.c
+192
View File
@@ -0,0 +1,192 @@
/*
* SPDX-License-Identifier: BSD-2-Clause
*
* Copyright (c) 2026 RISCstar Solutions.
*
* Authors:
* Dave Patel <dave.patel@riscstar.com>
*/
#include <sbi/riscv_asm.h>
#include <sbi/riscv_encoding.h>
#include <sbi/sbi_fp.h>
#if defined(__riscv_f) || defined(__riscv_d)
void sbi_fp_save(struct sbi_fp_context *dst)
{
unsigned long mstatus_orig;
if (!dst)
return;
mstatus_orig = csr_read_set(CSR_MSTATUS, MSTATUS_VS);
asm volatile(
#if defined(__riscv_d)
"fsd f0, 0(%0)\n"
"fsd f1, 8(%0)\n"
"fsd f2, 16(%0)\n"
"fsd f3, 24(%0)\n"
"fsd f4, 32(%0)\n"
"fsd f5, 40(%0)\n"
"fsd f6, 48(%0)\n"
"fsd f7, 56(%0)\n"
"fsd f8, 64(%0)\n"
"fsd f9, 72(%0)\n"
"fsd f10, 80(%0)\n"
"fsd f11, 88(%0)\n"
"fsd f12, 96(%0)\n"
"fsd f13, 104(%0)\n"
"fsd f14, 112(%0)\n"
"fsd f15, 120(%0)\n"
"fsd f16, 128(%0)\n"
"fsd f17, 136(%0)\n"
"fsd f18, 144(%0)\n"
"fsd f19, 152(%0)\n"
"fsd f20, 160(%0)\n"
"fsd f21, 168(%0)\n"
"fsd f22, 176(%0)\n"
"fsd f23, 184(%0)\n"
"fsd f24, 192(%0)\n"
"fsd f25, 200(%0)\n"
"fsd f26, 208(%0)\n"
"fsd f27, 216(%0)\n"
"fsd f28, 224(%0)\n"
"fsd f29, 232(%0)\n"
"fsd f30, 240(%0)\n"
"fsd f31, 248(%0)\n"
#else
"fsw f0, 0(%0)\n"
"fsw f1, 4(%0)\n"
"fsw f2, 8(%0)\n"
"fsw f3, 12(%0)\n"
"fsw f4, 16(%0)\n"
"fsw f5, 20(%0)\n"
"fsw f6, 24(%0)\n"
"fsw f7, 28(%0)\n"
"fsw f8, 32(%0)\n"
"fsw f9, 36(%0)\n"
"fsw f10, 40(%0)\n"
"fsw f11, 44(%0)\n"
"fsw f12, 48(%0)\n"
"fsw f13, 52(%0)\n"
"fsw f14, 56(%0)\n"
"fsw f15, 60(%0)\n"
"fsw f16, 64(%0)\n"
"fsw f17, 68(%0)\n"
"fsw f18, 72(%0)\n"
"fsw f19, 76(%0)\n"
"fsw f20, 80(%0)\n"
"fsw f21, 84(%0)\n"
"fsw f22, 88(%0)\n"
"fsw f23, 92(%0)\n"
"fsw f24, 96(%0)\n"
"fsw f25, 100(%0)\n"
"fsw f26, 104(%0)\n"
"fsw f27, 108(%0)\n"
"fsw f28, 112(%0)\n"
"fsw f29, 116(%0)\n"
"fsw f30, 120(%0)\n"
"fsw f31, 124(%0)\n"
#endif /* __riscv_d */
:
: "r"(dst->f)
: "memory"
);
dst->fcsr = csr_read(CSR_FCSR);
/* Restore original mstatus LAST */
csr_write(CSR_MSTATUS, mstatus_orig);
}
void sbi_fp_restore(const struct sbi_fp_context *src)
{
unsigned long mstatus_orig;
if (!src)
return;
/* Save original mstatus */
mstatus_orig = csr_read_set(CSR_MSTATUS, MSTATUS_FS);
asm volatile(
#if defined(__riscv_d)
"fld f0, 0(%0)\n"
"fld f1, 8(%0)\n"
"fld f2, 16(%0)\n"
"fld f3, 24(%0)\n"
"fld f4, 32(%0)\n"
"fld f5, 40(%0)\n"
"fld f6, 48(%0)\n"
"fld f7, 56(%0)\n"
"fld f8, 64(%0)\n"
"fld f9, 72(%0)\n"
"fld f10, 80(%0)\n"
"fld f11, 88(%0)\n"
"fld f12, 96(%0)\n"
"fld f13, 104(%0)\n"
"fld f14, 112(%0)\n"
"fld f15, 120(%0)\n"
"fld f16, 128(%0)\n"
"fld f17, 136(%0)\n"
"fld f18, 144(%0)\n"
"fld f19, 152(%0)\n"
"fld f20, 160(%0)\n"
"fld f21, 168(%0)\n"
"fld f22, 176(%0)\n"
"fld f23, 184(%0)\n"
"fld f24, 192(%0)\n"
"fld f25, 200(%0)\n"
"fld f26, 208(%0)\n"
"fld f27, 216(%0)\n"
"fld f28, 224(%0)\n"
"fld f29, 232(%0)\n"
"fld f30, 240(%0)\n"
"fld f31, 248(%0)\n"
#else
"flw f0, 0(%0)\n"
"flw f1, 4(%0)\n"
"flw f2, 8(%0)\n"
"flw f3, 12(%0)\n"
"flw f4, 16(%0)\n"
"flw f5, 20(%0)\n"
"flw f6, 24(%0)\n"
"flw f7, 28(%0)\n"
"flw f8, 32(%0)\n"
"flw f9, 36(%0)\n"
"flw f10, 40(%0)\n"
"flw f11, 44(%0)\n"
"flw f12, 48(%0)\n"
"flw f13, 52(%0)\n"
"flw f14, 56(%0)\n"
"flw f15, 60(%0)\n"
"flw f16, 64(%0)\n"
"flw f17, 68(%0)\n"
"flw f18, 72(%0)\n"
"flw f19, 76(%0)\n"
"flw f20, 80(%0)\n"
"flw f21, 84(%0)\n"
"flw f22, 88(%0)\n"
"flw f23, 92(%0)\n"
"flw f24, 96(%0)\n"
"flw f25, 100(%0)\n"
"flw f26, 104(%0)\n"
"flw f27, 108(%0)\n"
"flw f28, 112(%0)\n"
"flw f29, 116(%0)\n"
"flw f30, 120(%0)\n"
"flw f31, 124(%0)\n"
#endif /* __riscv_d */
:
: "r"(src->f)
: "memory"
);
csr_write(CSR_FCSR, src->fcsr);
/* Restore original mstatus LAST */
csr_write(CSR_MSTATUS, mstatus_orig);
}
#endif /* __riscv_f || __riscv_d */