1 files changed, 37 insertions, 0 deletions
diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
new file mode 100644
index 0000000..42f1eb4
--- /dev/null
+++ b/arch/riscv/include/asm/csr.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Copyright (C) 2026 Richard Qin */
+
+#ifndef _ASM_RISCV_CSR_H
+#define _ASM_RISCV_CSR_H
+
+/*
+ * RISC-V CSR (Control & Status Register) definitions used by the early
+ * boot / MMU-switch path.
+ *
+ * LumeOS-native subset of Linux arch/riscv/include/asm/csr.h.  Only the
+ * symbols head.S and mm/init.cc actually reference are defined — adding
+ * the rest is straightforward when new code needs them, and skipping the
+ * Linux ALTERNATIVE / vendor-extension machinery keeps the cascade flat.
+ */
+
+/* SATP (Supervisor Address Translation and Protection) layout — RV64 */
+#define SATP_PPN_MASK    0x00000FFFFFFFFFFFUL   /* bits [43:0] = root PPN */
+#define SATP_ASID_SHIFT  44
+#define SATP_MODE_SHIFT  60
+
+/* SATP MODE encodings (RV64) */
+#define SATP_MODE_BARE   (0UL << SATP_MODE_SHIFT)
+#define SATP_MODE_SV39   (8UL << SATP_MODE_SHIFT)
+#define SATP_MODE_SV48   (9UL << SATP_MODE_SHIFT)
+
+/* Compose a SATP value from a page-table physical address.
+ * Result: MODE | (root_ppn) where root_ppn = pgd_pa >> PAGE_SHIFT. */
+#define MAKE_SATP(mode, pgd_pa)  ((mode) | (((pgd_pa) >> 12) & SATP_PPN_MASK))
+
+/* SSTATUS bits we touch at boot — disable FP / vector at entry so that an
+ * accidental FP / V instruction in early code traps cleanly rather than
+ * silently using dirty state from before reset. */
+#define SR_FS_OFF        (0UL << 13)
+#define SR_VS_OFF        (0UL << 9)
+
+#endif /* _ASM_RISCV_CSR_H */