lib: utils: Add a fdt_reserved_memory_fixup() helper

Add a helper routine to insert a child node of the reserved memory
node in the device tree that describes the protected memory region
done by OpenSBI via PMP.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>

include/sbi_utils/fdt/fdt_helper.h

@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: BSD-2-Clause
+/*
+ * fdt_helper.h - Flat Device Tree manipulation helper routines
+ * Implement helper routines on top of libfdt for OpenSBI usage
+ *
+ * Copyright (C) 2020 Bin Meng <bmeng.cn@gmail.com>
+ */
+
+#ifndef __FDT_HELPER_H__
+#define __FDT_HELPER_H__
+
+/**
+ * Fix up the reserved memory node in the device tree
+ *
+ * This routine inserts a child node of the reserved memory node in the device
+ * tree that describes the protected memory region done by OpenSBI via PMP.
+ *
+ * It is recommended that platform codes call this helper in their final_init()
+ *
+ * @param fdt: device tree blob
+ * @return zero on success and -ve on failure
+ */
+int fdt_reserved_memory_fixup(void *fdt);
+
+#endif /* __FDT_HELPER_H__ */

lib/utils/fdt/fdt_helper.c

@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: BSD-2-Clause
+/*
+ * fdt_helper.c - Flat Device Tree manipulation helper routines
+ * Implement helper routines on top of libfdt for OpenSBI usage
+ *
+ * Copyright (C) 2020 Bin Meng <bmeng.cn@gmail.com>
+ */
+
+#include <libfdt.h>
+#include <sbi/riscv_asm.h>
+#include <sbi/sbi_console.h>
+#include <sbi/sbi_platform.h>
+#include <sbi/sbi_scratch.h>
+
+/**
+ * We use PMP to protect OpenSBI firmware to safe-guard it from buggy S-mode
+ * software, see pmp_init() in lib/sbi/sbi_hart.c. The protected memory region
+ * information needs to be conveyed to S-mode software (e.g.: operating system)
+ * via some well-known method.
+ *
+ * With device tree, this can be done by inserting a child node of the reserved
+ * memory node which is used to specify one or more regions of reserved memory.
+ *
+ * For the reserved memory node bindings, see Linux kernel documentation at
+ * Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
+ *
+ * Some additional memory spaces may be protected by platform codes via PMP as
+ * well, and corresponding child nodes will be inserted.
+ */
+int fdt_reserved_memory_fixup(void *fdt)
+{
+	struct sbi_scratch *scratch = sbi_scratch_thishart_ptr();
+	const struct sbi_platform *plat = sbi_platform_ptr(scratch);
+	unsigned long prot, addr, size;
+	int na = fdt_address_cells(fdt, 0);
+	int ns = fdt_size_cells(fdt, 0);
+	fdt32_t addr_high, addr_low;
+	fdt32_t size_high, size_low;
+	fdt32_t reg[4];
+	fdt32_t *val;
+	char name[32];
+	int parent, subnode;
+	int i, j;
+	int err;
+
+	if (!sbi_platform_has_pmp(plat))
+		return 0;
+
+	/* expand the device tree to accommodate new node */
+	err  = fdt_open_into(fdt, fdt, fdt_totalsize(fdt) + 256);
+	if (err < 0)
+		return err;
+
+	/* try to locate the reserved memory node */
+	parent = fdt_path_offset(fdt, "/reserved-memory");
+	if (parent < 0) {
+		/* if such node does not exist, create one */
+		parent = fdt_add_subnode(fdt, 0, "reserved-memory");
+		if (parent < 0)
+			return parent;
+
+		/*
+		 * reserved-memory node has 3 required properties:
+		 * - #address-cells: the same value as the root node
+		 * - #size-cells: the same value as the root node
+		 * - ranges: should be empty
+		 */
+
+		err = fdt_setprop_empty(fdt, parent, "ranges");
+		if (err < 0)
+			return err;
+
+		err = fdt_setprop_u32(fdt, parent, "#size-cells", ns);
+		if (err < 0)
+			return err;
+
+		err = fdt_setprop_u32(fdt, parent, "#address-cells", na);
+		if (err < 0)
+			return err;
+	}
+
+	/*
+	 * We assume the given device tree does not contain any memory region
+	 * child node protected by PMP. Normally PMP programming happens at
+	 * M-mode firmware. The memory space used by OpenSBI is protected.
+	 * Some additional memory spaces may be protected by platform codes.
+	 *
+	 * With above assumption, we create child nodes directly.
+	 */
+
+	for (i = 0, j = 0; i < PMP_COUNT; i++) {
+		pmp_get(i, &prot, &addr, &size);
+		if (!(prot & PMP_A))
+			continue;
+		if (!(prot & (PMP_R | PMP_W | PMP_X))) {
+			addr_high = (u64)addr >> 32;
+			addr_low = addr;
+			size_high = (u64)size >> 32;
+			size_low = size;
+
+			if (na > 1 && addr_high)
+				sbi_snprintf(name, sizeof(name),
+					     "mmode_pmp%d@%x,%x", j,
+					     addr_high, addr_low);
+			else
+				sbi_snprintf(name, sizeof(name),
+					     "mmode_pmp%d@%x", j,
+					     addr_low);
+
+			subnode = fdt_add_subnode(fdt, parent, name);
+			if (subnode < 0)
+				return subnode;
+
+			/*
+			 * Tell operating system not to create a virtual
+			 * mapping of the region as part of its standard
+			 * mapping of system memory.
+			 */
+			err = fdt_setprop_empty(fdt, subnode, "no-map");
+			if (err < 0)
+				return err;
+
+			/* encode the <reg> property value */
+			val = reg;
+			if (na > 1)
+				*val++ = cpu_to_fdt32(addr_high);
+			*val++ = cpu_to_fdt32(addr_low);
+			if (ns > 1)
+				*val++ = cpu_to_fdt32(size_high);
+			*val++ = cpu_to_fdt32(size_low);
+
+			err = fdt_setprop(fdt, subnode, "reg", reg,
+					  (na + ns) * sizeof(fdt32_t));
+			if (err < 0)
+				return err;
+
+			j++;
+		}
+	}
+
+	return 0;
+}

lib/utils/fdt/objects.mk

@@ -0,0 +1,7 @@
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+# Copyright (C) 2020 Bin Meng <bmeng.cn@gmail.com>
+#
+
+libsbiutils-objs-y += fdt/fdt_helper.o