command: Add constants for cmd_get_data_size string / error

At present these values are open-coded in a few places. Add constants so
the meaning is clear.

Also add a comment to cmd_get_data_size()

Signed-off-by: Simon Glass <sjg@chromium.org>

cmd/itest.c

@@ -197,10 +197,10 @@ static int do_itest(struct cmd_tbl *cmdtp, int flag, int argc,
 #endif
 		value = binary_test (argv[2], argv[1], argv[3], w);
 		break;
-	case -2:
+	case CMD_DATA_SIZE_STR:
 		value = binary_test (argv[2], argv[1], argv[3], 0);
 		break;
-	case -1:
+	case CMD_DATA_SIZE_ERR:
 	default:
 		puts("Invalid data width specifier\n");
 		value = 0;

cmd/mem.c

@@ -393,7 +393,7 @@ static int do_mem_search(struct cmd_tbl *cmdtp, int flag, int argc,
 		 * Defaults to long if no or incorrect specification.
 		 */
 		size = cmd_get_data_size(argv[0], 4);
-		if (size < 0 && size != -2 /* string */)
+		if (size < 0 && size != CMD_DATA_SIZE_STR)
 			return 1;
 
 		argc--;

common/command.c

@@ -475,13 +475,13 @@ int cmd_get_data_size(char* arg, int default_size)
 		case 'l':
 			return 4;
 		case 's':
-			return -2;
+			return CMD_DATA_SIZE_STR;
 		case 'q':
 			if (MEM_SUPPORT_64BIT_DATA)
 				return 8;
 			/* no break */
 		default:
-			return -1;
+			return CMD_DATA_SIZE_ERR;
 		}
 	}
 	return default_size;

include/command.h

@@ -117,7 +117,31 @@ int cmd_process_error(struct cmd_tbl *cmdtp, int err);
 	defined(CONFIG_CMD_PCI) || \
 	defined(CONFIG_CMD_SETEXPR)
 #define CMD_DATA_SIZE
-extern int cmd_get_data_size(char* arg, int default_size);
+#define CMD_DATA_SIZE_ERR	(-1)
+#define CMD_DATA_SIZE_STR	(-2)
+
+/**
+ * cmd_get_data_size() - Get the data-size specifier from a command
+ *
+ * This reads a '.x' size specifier appended to a command. For example 'md.b'
+ * is the 'md' command with a '.b' specifier, meaning that the command should
+ * use bytes.
+ *
+ * Valid characters are:
+ *
+ *	b - byte
+ *	w - word (16 bits)
+ *	l - long (32 bits)
+ *	q - quad (64 bits)
+ *	s - string
+ *
+ * @arg: Pointers to the command to check. If a valid specifier is present it
+ *	will be the last character of the string, following a '.'
+ * @default_size: Default size to return if there is no specifier
+ * @return data size in bytes (1, 2, 4, 8) or CMD_DATA_SIZE_ERR for an invalid
+ *	character, or CMD_DATA_SIZE_STR for a string
+ */
+int cmd_get_data_size(char *arg, int default_size);
 #endif
 
 #ifdef CONFIG_CMD_BOOTD