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

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>

include/sbi/sbi_fp.h

@@ -0,0 +1,35 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2026 RISCstar Solutions.
+ *
+ * Authors:
+ *   Dave Patel <dave.patel@riscstar.com>
+ */
+#ifndef __SBI_FP_H__
+#define __SBI_FP_H__
+
+#include <sbi/sbi_types.h>
+
+struct sbi_fp_context {
+#if __riscv_d
+	uint64_t f[32];
+#else
+	uint32_t f[32];
+#endif
+	unsigned long fcsr;
+};
+
+#if defined(__riscv_f) || defined(__riscv_d)
+void sbi_fp_save(struct sbi_fp_context *dst);
+void sbi_fp_restore(const struct sbi_fp_context *src);
+#else
+static inline void sbi_fp_save(struct sbi_fp_context *dst)
+{
+}
+static inline void sbi_fp_restore(const struct sbi_fp_context *src)
+{
+}
+#endif /* __riscv_f || __riscv_d */
+
+#endif /*__SBI_FP_H__ */

lib/sbi/objects.mk

@@ -103,3 +103,4 @@ libsbi-objs-y += sbi_unpriv.o
 libsbi-objs-y += sbi_expected_trap.o
 libsbi-objs-y += sbi_cppc.o
 libsbi-objs-$(CC_SUPPORT_VECTOR) += sbi_vector.o
+libsbi-objs-y += sbi_fp.o

lib/sbi/sbi_fp.c

@@ -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 */