RISC-V: Implement compile-time fixed mappings

This patch implements compile-time virtual to physical mappings. These
compile-time fixed mappings can be used by earlycon, ACPI, and early
ioremap for creating fixed mappings when FIX_EARLYCON_MEM=y.

To start with, we have enabled compile-time fixed mappings for earlycon.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Palmer Dabbelt <palmer@sifive.com>

1 files changed, 44 insertions, 0 deletions

diff --git a/arch/riscv/include/asm/fixmap.h b/arch/riscv/include/asm/fixmap.h
new file mode 100644
index 000000000000..57afe604b495
--- /dev/null
+++ b/arch/riscv/include/asm/fixmap.h
@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2019 Western Digital Corporation or its affiliates.
+ */
+
+#ifndef _ASM_RISCV_FIXMAP_H
+#define _ASM_RISCV_FIXMAP_H
+
+#include <linux/kernel.h>
+#include <linux/sizes.h>
+#include <asm/page.h>
+#include <asm/pgtable.h>
+
+/*
+ * Here we define all the compile-time 'special' virtual addresses.
+ * The point is to have a constant address at compile time, but to
+ * set the physical address only in the boot process.
+ *
+ * These 'compile-time allocated' memory buffers are page-sized. Use
+ * set_fixmap(idx,phys) to associate physical memory with fixmap indices.
+ */
+enum fixed_addresses {
+	FIX_HOLE,
+	FIX_EARLYCON_MEM_BASE,
+	__end_of_fixed_addresses
+};
+
+#define FIXADDR_SIZE		(__end_of_fixed_addresses * PAGE_SIZE)
+#define FIXADDR_TOP		(PAGE_OFFSET)
+#define FIXADDR_START		(FIXADDR_TOP - FIXADDR_SIZE)
+
+#define FIXMAP_PAGE_IO		PAGE_KERNEL
+
+#define __early_set_fixmap	__set_fixmap
+
+#define __late_set_fixmap	__set_fixmap
+#define __late_clear_fixmap(idx) __set_fixmap((idx), 0, FIXMAP_PAGE_CLEAR)
+
+extern void __set_fixmap(enum fixed_addresses idx,
+			 phys_addr_t phys, pgprot_t prot);
+
+#include <asm-generic/fixmap.h>
+
+#endif /* _ASM_RISCV_FIXMAP_H */