Dynamic cfg: Introduce fdt wrappers

Change-Id: I9b1cdaf2430a1998a69aa366ea1461224a3d43dc
Co-Authoured-by: Jeenu Viswambharan <Jeenu.Viswambharan@arm.com>
Signed-off-by: Soby Mathew <soby.mathew@arm.com>

common/fdt_wrappers.c

@@ -0,0 +1,96 @@
+/*
+ * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+/* Helper functions to offer easier navigation of Device Tree Blob */
+
+#include <assert.h>
+#include <debug.h>
+#include <fdt_wrappers.h>
+#include <libfdt.h>
+
+/*
+ * Read cells from a given property of the given node. At most 2 cells of the
+ * property are read, and pointer is updated. Returns 0 on success, and -1 upon
+ * error
+ */
+int fdtw_read_cells(const void *dtb, int node, const char *prop,
+		unsigned int cells, void *value)
+{
+	const uint32_t *value_ptr;
+	uint32_t hi = 0, lo;
+	int value_len;
+
+	assert(dtb);
+	assert(prop);
+	assert(value);
+	assert(node >= 0);
+
+	/* We expect either 1 or 2 cell property */
+	assert(cells <= 2);
+
+	/* Access property and obtain its length (in bytes) */
+	value_ptr = fdt_getprop_namelen(dtb, node, prop, strlen(prop),
+			&value_len);
+	if (value_ptr == NULL) {
+		WARN("Couldn't find property %s in dtb\n", prop);
+		return -1;
+	}
+
+
+	/* Verify that property length accords with cell length */
+	if (NCELLS(value_len) != cells) {
+		WARN("Property length mismatch\n");
+		return -1;
+	}
+
+	if (cells == 2) {
+		hi = fdt32_to_cpu(*value_ptr);
+		value_ptr++;
+	}
+
+	lo = fdt32_to_cpu(*value_ptr);
+
+	if (cells == 2)
+		*((uint64_t *) value) = ((uint64_t) hi << 32) | lo;
+	else
+		*((uint32_t *) value) = lo;
+
+	return 0;
+}
+
+/*
+ * Write cells in place to a given property of the given node. At most 2 cells
+ * of the property are written. Returns 0 on success, and -1 upon error.
+ */
+int fdtw_write_inplace_cells(void *dtb, int node, const char *prop,
+		unsigned int cells, void *value)
+{
+	int err, len;
+
+	assert(dtb);
+	assert(prop);
+	assert(value);
+	assert(node >= 0);
+
+	/* We expect either 1 or 2 cell property */
+	assert(cells <= 2);
+
+	if (cells == 2)
+		*(uint64_t *)value = cpu_to_fdt64(*(uint64_t *)value);
+	else
+		*(uint32_t *)value = cpu_to_fdt32(*(uint32_t *)value);
+
+	len = cells * 4;
+
+	/* Set property value in place */
+	err = fdt_setprop_inplace(dtb, node, prop, value, len);
+	if (err != 0) {
+		WARN("Modify property %s failed with error %d\n", prop, err);
+		return -1;
+	}
+
+	return 0;
+}

include/common/fdt_wrappers.h

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+/* Helper functions to offer easier navigation of Device Tree Blob */
+
+#ifndef __FDT_WRAPPERS__
+#define __FDT_WRAPPERS__
+
+/* Number of cells, given total length in bytes. Each cell is 4 bytes long */
+#define NCELLS(l) (l / 4)
+
+int fdtw_read_cells(const void *dtb, int node, const char *prop,
+		unsigned int cells, void *value);
+int fdtw_write_inplace_cells(void *dtb, int node, const char *prop,
+		unsigned int cells, void *value);
+#endif /* __FDT_WRAPPERS__ */