feat(fdt): introduce wrapper function to read DT UUIDs

TF-A does not have the capability to read UUIDs in string form
from the device tree. This capability is useful for readability,
so add a wrapper function, fdtw_read_uuid() to parse UUIDs from
the DT.
This function should parse a string of the form:

"aabbccdd-eeff-4099-8877-665544332211"

to the byte sequence in memory:

[aa bb cc dd ee ff 40 99 88 77 66 55 44 33 22 11]

Change-Id: I99a92fbeb40f4f4713f3458b36cb3863354d2bdf
Signed-off-by: David Horstmann <david.horstmann@arm.com>

common/fdt_wrappers.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2018-2021, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -7,12 +7,14 @@
 /* Helper functions to offer easier navigation of Device Tree Blob */
 
 #include <assert.h>
+#include <errno.h>
 #include <string.h>
 
 #include <libfdt.h>
 
 #include <common/debug.h>
 #include <common/fdt_wrappers.h>
+#include <common/uuid.h>
 
 /*
  * Read cells from a given property of the given node. Any number of 32-bit
@@ -151,6 +153,39 @@ int fdtw_read_string(const void *dtb, int node, const char *prop,
 	return 0;
 }
 
+/*
+ * Read UUID from a given property of the given node. Returns 0 on success,
+ * and a negative value upon error.
+ */
+int fdtw_read_uuid(const void *dtb, int node, const char *prop,
+		   unsigned int length, uint8_t *uuid)
+{
+	/* Buffer for UUID string (plus NUL terminator) */
+	char uuid_string[UUID_STRING_LENGTH + 1U];
+	int err;
+
+	assert(dtb != NULL);
+	assert(prop != NULL);
+	assert(uuid != NULL);
+	assert(node >= 0);
+
+	if (length < UUID_BYTES_LENGTH) {
+		return -EINVAL;
+	}
+
+	err = fdtw_read_string(dtb, node, prop, uuid_string,
+			       UUID_STRING_LENGTH + 1U);
+	if (err != 0) {
+		return err;
+	}
+
+	if (read_uuid(uuid, uuid_string) != 0) {
+		return -FDT_ERR_BADVALUE;
+	}
+
+	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.

common/uuid.c

@@ -0,0 +1,133 @@
+/*
+ * Copyright (c) 2021, Arm Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <assert.h>
+#include <errno.h>
+#include <stdint.h>
+#include <string.h>
+
+#include <common/debug.h>
+#include <common/uuid.h>
+
+/* Return the hex nibble value of a char */
+static int8_t hex_val(char hex)
+{
+	int8_t val = 0;
+
+	if ((hex >= '0') && (hex <= '9')) {
+		val = (int8_t)(hex - '0');
+	} else if ((hex >= 'a') && (hex <= 'f')) {
+		val = (int8_t)(hex - 'a' + 0xa);
+	} else if ((hex >= 'A') && (hex <= 'F')) {
+		val = (int8_t)(hex - 'A' + 0xa);
+	} else {
+		val = -1;
+	}
+
+	return val;
+}
+
+/*
+ * Read hex_src_len hex characters from hex_src, convert to bytes and
+ * store in buffer pointed to by dest
+ */
+static int read_hex(uint8_t *dest, char *hex_src, unsigned int hex_src_len)
+{
+	int8_t nibble;
+	uint8_t byte;
+
+	/*
+	 * The string length must be a multiple of 2 to represent an
+	 * exact number of bytes.
+	 */
+	assert((hex_src_len % 2U) == 0U);
+
+	for (unsigned int i = 0U; i < (hex_src_len / 2U); i++) {
+		nibble = 0;
+		byte = 0U;
+
+		nibble = hex_val(hex_src[2U * i]);
+		if (nibble < 0) {
+			return -1;
+		}
+		byte = (uint8_t)nibble;
+		byte <<= 4U;
+
+		nibble = hex_val(hex_src[(2U * i) + 1U]);
+		if (nibble < 0) {
+			return -1;
+		}
+		byte |= (uint8_t)nibble;
+
+		*dest = byte;
+		dest++;
+	}
+
+	return 0;
+}
+
+/* Parse UUIDs of the form aabbccdd-eeff-4099-8877-665544332211 */
+int read_uuid(uint8_t *dest, char *uuid)
+{
+	int err;
+
+	/* Check that we have enough characters */
+	if (strnlen(uuid, UUID_STRING_LENGTH) != UUID_STRING_LENGTH) {
+		WARN("UUID string is too short\n");
+		return -EINVAL;
+	}
+
+	/* aabbccdd */
+	err = read_hex(dest, uuid, 8);
+	uuid += 8;
+	dest += 4;
+
+	/* Check for '-' */
+	err |= ((*uuid == '-') ? 0 : -1);
+	uuid++;
+
+	/* eeff */
+	err |= read_hex(dest, uuid, 4);
+	uuid += 4;
+	dest += 2;
+
+	/* Check for '-' */
+	err |= ((*uuid == '-') ? 0 : -1);
+	uuid++;
+
+	/* 4099 */
+	err |= read_hex(dest, uuid, 4);
+	uuid += 4;
+	dest += 2;
+
+	/* Check for '-' */
+	err |= ((*uuid == '-') ? 0 : -1);
+	uuid++;
+
+	/* 8877 */
+	err |= read_hex(dest, uuid, 4);
+	uuid += 4;
+	dest += 2;
+
+	/* Check for '-' */
+	err |= ((*uuid == '-') ? 0 : -1);
+	uuid++;
+
+	/* 665544332211 */
+	err |= read_hex(dest, uuid, 12);
+	uuid += 12;
+	dest += 6;
+
+	if (err < 0) {
+		WARN("Error parsing UUID\n");
+		/* Clear the buffer on error */
+		memset((void *)dest, '\0', UUID_BYTES_LENGTH * sizeof(uint8_t));
+		return -EINVAL;
+	}
+
+	return 0;
+}
+

include/common/fdt_wrappers.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2018-2021, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -24,6 +24,8 @@ int fdt_read_uint32_array(const void *dtb, int node, const char *prop_name,
 			  unsigned int cells, uint32_t *value);
 int fdtw_read_string(const void *dtb, int node, const char *prop,
 		char *str, size_t size);
+int fdtw_read_uuid(const void *dtb, int node, const char *prop,
+		   unsigned int length, uint8_t *uuid);
 int fdtw_write_inplace_cells(void *dtb, int node, const char *prop,
 		unsigned int cells, void *value);
 int fdtw_read_bytes(const void *dtb, int node, const char *prop,

include/common/uuid.h

@@ -0,0 +1,15 @@
+/*
+ * Copyright (c) 2021, Arm Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef UUID_H
+#define UUID_H
+
+#define UUID_BYTES_LENGTH	16
+#define UUID_STRING_LENGTH	36
+
+int read_uuid(uint8_t *dest, char *uuid);
+
+#endif /* UUID_H */