From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jon Loeliger <jdl-CYoMK+44s/E@public.gmane.org>
Subject: [PATCH 8/9 V3] Add documentation for the new DTS language.
Date: Fri, 26 Sep 2008 15:25:47 -0500
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List-Id: devicetree@vger.kernel.org

From: Jon Loeliger <jdl-KZfg59tc24xl57MIdRCFDg@public.gmane.org>

Signed-off-by: Jon Loeliger <jdl-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
---
 Documentation/manual.txt |  500 ++++++++++++++++++++++++++++++++++++++++++----
 1 files changed, 463 insertions(+), 37 deletions(-)

diff --git a/Documentation/manual.txt b/Documentation/manual.txt
index b957662..ac56309 100644
--- a/Documentation/manual.txt
+++ b/Documentation/manual.txt
@@ -105,13 +105,21 @@ Options:
     -q
 	Quiet: -q suppress warnings, -qq errors, -qqq all
 
+    -D <id>
+    -D <id>=<value>
+	Introduce a constant definition for symbol <id> with
+	possible initial value given by <value>.  The RHS
+	should be a literal number or string value.
+
+    -p <padsize>
+	Add at least <padsize> additional space to the DTB image.
+
     -R <number>
 	Make space for <number> reserve map entries
 	Relevant for dtb and asm output only.
 
     -S <bytes>
-	Ensure the blob at least <bytes> long, adding additional
-	space if needed.
+	Deprecated option.
 
     -v
 	Print DTC version and exit.
@@ -131,47 +139,338 @@ Additionally, dtc performs various sanity checks on the tree.
 
 4) Device Tree Source file
 
-4.1) Overview
 
-Here is a very rough overview of the layout of a DTS source file:
+4.1) DTS Lexical Components
+
+Property and node names		[a-zA-Z0-9,._+*#?@-]+
+Identifiers			\\[a-zA-Z_][a-zA-Z0-9_]*
+Labels				[a-zA-Z_][a-zA-Z0-9_]*
+Strings				<C-style-double-quoted-strings>
+Comments			Both /* ... */ and // style are supported
+Numeric literals		<C-style-integer-numbers>
+Bytes				[0-9a-fA-F][0-9a-fA-F]
+
+Keywords:
+	else
+	for
+	if
+	in
+	return
+	void
+	/const/
+	/define/
+	/incbin/
+
+C-style expression operators:
+	<<
+	>>
+	<=
+	>=
+	==
+	!=
+	&&
+	||
+	+
+	-
+	*
+	/
+	%
+
+Additional tokens:
+	..
+	:=
+	{
+	}
+	,
+	&
+
+
+These constructs are handled and eliminated purely at the
+lexical level and do not appear in the grammar proper:
+
+    - Source files included using the syntax:
+
+        /include/ "filename"
+
+    - Both classic C style and C++ style comments are supported.
+      Comments don't nest.
+      For example, given:
+
+	1    /*
+	2     *  asdasdasd  // asdasdad
+	3     //   */
+	4    asasd
+	5     */
+      The // comment on line 3 is not effective and is ignored.
+      The original /* comment ends on line 3.  Line 5 is in error.
+
+      And given:
+
+	1    // /*
+	2     *  asdasdasd  // asdasdad
+	3     */
+
+      The // comment on line 1 hides the opening /*.
+      Line 2 is in error.
+
+
+4.2) DTS Grammar
+
+Here is a very rough overview of the grammar of a DTS source file:
+
+
+    sourcefile:
+		'/dts-v1/' ';' possibly_empty_list_of_declarations devicetree
+
+    declaration:
+		  memreserve
+		| constdef
+		| funcdef
+
+    memreserve:	label '/memreserve/' addr addr ';'
+
+    constdef:	'/const/' identifier '=' expr ';'
+
+    funcdef:	'/define/' propnodename paramdecls statement_block
+
+    paramdecls:	'(' possibly_empty_paramdecl_list ')'
+
+    paramdecl: identifier
+
+    devicetree:   '/' statement_block
+
+    statement_block: '{' possibly_empty_list_of_statements '}'
+
+    statement:
+		  subnode
+		| for_statement
+		| if_statement
+		| return_statement
+		| assign_statement
+		| property_definition
+		| statement_block
+		| ';'
+
+    subnode:
+		  node_label expr statement_block ';'
+		|      label expr statement_block ';'
+		|            expr statement_block ';'
+
+    for_statement:
+		'for' identifier 'in' expr '..' expr statement_block
+
+    if_statement:
+		  'if' '(' expr ')' statement_block
+		| 'if' '(' expr ')' statement_block 'else' statement_block
+
+    return_statement: 'return' expr ';'
+
+    assign_statement: identifier ':=' expr ';'
+
+    property_definition:
+		  optional_label expr ';'
+		| optional_label expr '=' list_of_property_data_and_labels ';'
 
+    list_of_property_data_and_labels:
+		  STRING
+		| '<' possibly_empty_list_of_cell_values_and_labels '>'
+		| '[' possibly_empty_list_of_byte_values_and_labels ']'
+		| label
+		| '/incbin/' '(' expr ')'
+		| '/incbin/' '(' expr ',' expr ',' expr ')'
 
-    sourcefile:   list_of_memreserve devicetree
+    cell_value:
+		  expr_primary
+		| '&' '(' expr ')'
+		| '&' phandle_reference
+		| label
 
-    memreserve:   label 'memreserve' ADDR ADDR ';'
-		| label 'memreserve' ADDR '-' ADDR ';'
 
-    devicetree:   '/' nodedef
+    expr:
+          expr_primary
+	| expr '?' expr ':' expr
+	| expr expr_oper expr
 
-    nodedef:      '{' list_of_property list_of_subnode '}' ';'
+    expr_oper:
+	||
+        &&
+	|
+	^
+	&
+	==
+	< | > | <= | >=
+	<< | >>
+	+ | -
+	* | / | %
+	- | ~ | !
+        '(' ')' | '(' non_empty_list_of_param_exprs ')'
 
-    property:     label PROPNAME '=' propdata ';'
+    expr_primary:
+	  literal
+	| string
+	| propnodename
+	| identifier
+	| '(' expr ')'
 
-    propdata:     STRING
-		| '<' list_of_cells '>'
-		| '[' list_of_bytes ']'
+    addr:	expr
 
-    subnode:      label nodename nodedef
+    node_label:	expr ':'
 
-That structure forms a hierarchical layout of nodes and properties
-rooted at an initial node as:
+    propnodename: <1275-property-name>
+
+    identifier:	'\'-<C style name>
+
+    literal:	<C style number>
+    byte:	<exactly two hex digits>
+    string:	<C style string>
+    label:	'&'-<label name>-':'
+
+
+4.2) Overview
+
+The DTS source file begins with the '/dts-v1/' token to state
+that it is using "Version 1" style source files.
+
+Any declarations are executed in order, and can use the
+effects of earlier declarations.
+
+All declarations must precede the required root node definition,
+which is introduced with the '/'-named node:
 
     / {
+	...
     }
 
-Both classic C style and C++ style comments are supported.
+The statement-block structure forms a hierarchical layout of nodes
+and properties along with some control-statements that allow for
+repeated and alternate statement blocks.
+
+
+4.3) Declarations
+
+An arbitrary list of declarations can be made between '/dts-v1/'
+and the beginning of the root node.  These declarations are
+introduced in order.
+
+
+4.3.1) Memory Reservations
+
+A memory reservation is a declaration that a block of memory
+from the first address expression, with a size given by the
+second address expression, is to be "reserved" and not used
+by the kernel.  These address ranges are passed through to
+the DTB to the kernel.
+
+
+4.3.2) Function Definitions
+
+A function definition can be introduced using /define/.
+These definitions are just "stored" and then later invoked as
+either a subroutine in a statement context, or as a function
+with a return value in an expression context.
 
-Source files may be directly included using the syntax:
+Functions declare the number of formal parameters which will
+be passed in at the call site, and must match one-to-one.
 
-    /include/ "filename"
+Any property definitions generated by the function are emitted
+into the caller's context at the point of the call.
 
+Any node definitions generated by the function are emitted
+into the caller's context at the point of the call.
 
-4.2) Properties
 
-Properties are named, possibly labeled, values.  Each value
-is one of:
+4.3.3) Constant Definitions
 
-    - A null-teminated C-like string,
+Constant definitions introduce a named identifier into the outer-most
+symbol scope.  The constants can not be changed by later assignment
+statements, though they can be hidden.  (Be careful.)
+
+Constants may be expressions yielding constant numeric or strings
+values.  It is an error for them not to be evaluatable at their
+point of definition.
+
+Constant definitions may also be introduced from the command line
+using the '-D var=value" options.  They will be placed into the
+same outer-most scope.  Constant definitions from the command line
+override the definitions within the source file, but with a warning.
+
+
+4.4) Statements
+
+A statement block is simply a list of sequentially executed
+statements introduced with a required opening brace and terminated
+with a required closing brace.
+
+4.4.1) Subnodes
+
+Node may contain sub-nodes to obtain a hierarchical structure.
+
+For example:
+
+    - A child node named "childnode" whose unit name is
+      "childnode at address".  It it turn has a string property
+      called "childprop".
+
+	childnode@address {
+	    childprop = "hello\n";
+	};
+
+
+4.4.2) 'for' Statement
+
+The 'for' statement provides iterative execution of a
+block of statements.
+
+The lower bound of the range is evaluated once, and the
+upper bound is evaluated once.
+
+A new scope that contains the loop variable is created
+and pushed onto the symbol table scope stack.  The loop
+variable is initialized with the lower bound value.
+
+The statement block is executed once for each inclusive value
+in the given range in increasing order.
+
+After the loop terminates, the loop variable scope is popped.
+
+
+4.4.3) 'if' Statement
+
+The 'if' statement provides alternate execution flow paths.
+The expression is evaluated once, and if non-zero, the fist
+statement block is executed, otherwise the 'else' block of
+statements is executed if present.
+
+
+4.4.4) 'return' Statement
+
+Inside a function definition, the 'return' statement allows
+a value to be passed back to the caller.  The return expression
+is evaluated once, in the context of the function's scope,
+and its resultant value is made available as the function's
+return result.
+
+
+4.4.5) Assign Statement
+
+The ':=' operator allows assignment to non-constant identifiers.
+
+The identifiers can be either formal parameters or variable as
+found by the searching using the dynamic symbol table scoping rules.
+
+An assignment to an otherwise unknown identifier causes that
+identifier to be introduced into the current scope.
+
+You can't assign to /constant/ identifiers (except in the initial
+definition of them).
+
+
+4.4.6) Property Definition
+
+Properties are named, possibly labeled, values.
+Each value within a property is one of:
+
+    - A null-terminated C-like string,
     - A numeric value fitting in 32 bits,
     - A list of 32-bit values
     - A byte sequence
@@ -195,27 +494,126 @@ Here are some example property definitions:
 	property4 = [0a 0b 0c 0d de ea ad be ef];
 
 
-Node may contain sub-nodes to obtain a hierarchical structure.
-For example:
+4.4.7) Subroutine calls
 
-    - A child node named "childnode" whose unit name is
-      "childnode at address".  It it turn has a string property
-      called "childprop".
+An expression at the statement level should be a function call,
+though it might be considered as just a "subroutine call" as
+any return value is thrown away.
 
-	childnode@addresss {
-	    childprop = "hello\n";
-	};
+Invocation of the function introduces a symbol table scope
+in which the formal paramters are introduced and bound.
+Initial values for the formals are obtained by evaluating
+the actual parameters, in order, and using a copy-in binding.
+
+Any incidental (dynamically occurring) assignment to an
+otherwise unknown identifier will cause the introduction of
+a new variable in the function's execution scope.
+
+Any property definitions generated by the function are emitted
+into the caller's context at the point of the subroutine call.
+
+Any node definitions generated by the function are emitted
+into the caller's context at the point of the subroutine call.
+
+Any return value from a return statement is thrown away.
 
+Execution control is returned to the point of the call.
 
-By default, all numeric values are hexadecimal.  Alternate bases
-may be specified using a prefix "d#" for decimal, "b#" for binary,
-and "o#" for octal.
 
-Strings support common escape sequences from C: "\n", "\t", "\r",
-"\(octal value)", "\x(hex value)".
+4.5) Expressions
 
+Basically, expressions follow C conventions.  However, there
+are no assignment operations such as +=, or pre-/post-
+increment/decrement.
 
-4.3) Labels and References
+The '%' operation is a modulus operation for integers, and
+a string concatenation operation if at least one of the operands
+is determined to be a string value.
+
+
+4.5.1) Expressions
+
+Pretend it is C and see how close we get.
+
+
+4.5.2) Function Invocations
+
+A previously defined function may be invoked from within an
+expression.  A "return" statement should be used to return
+a resulting expression value to the caller's context.
+
+Invocation of the function introduces a symbol table scope
+in which the formal parameters are introduced and bound.
+Initial values for the formals are obtained by evaluating
+the actual parameters, in order, and using a copy-in binding.
+
+Any incidental (dynamically occurring) assignment to an
+otherwise unknown identifier will cause the introduciton of
+a new variable in the function's execution scope.
+
+Any property definitions generated by the function are emitted
+into the caller's context at the point of the subroutine call.
+
+Any node definitions generated by the function are emitted
+into the caller's context at the point of the subroutine call.
+
+Any return value from a return statement is used as the result
+of the function call within the context of the original expression.
+
+Execution control is returned to the point of the call.
+
+
+4.5.3) Builtin Functions
+
+There are a few builtin function names;
+
+    join()	Concatenate and return a list of expression
+		as a string.  Non-string arguments are coerced
+		into being a string.
+
+    hexstr()	Format and return a hex string representation
+		of the one parameter without a leading '0x'.
+
+While not here yet, /incbin/ should be converted into a builtin.
+
+
+4.5.4) Literal Numbers
+
+Literal numbers follow C conventions.  Specifically, they are
+base-ten by default, but can be hexadecimal, binary or octal
+with a leading 0x or 0X, 0b or OB, or a simple leading zero,
+respectively.
+
+There is no support for floating point representations at all.
+
+Most math and expression handling is assumed to be 64-bit, but
+a cell-context may force a 32-bit container instead.
+
+
+4.5.5) Literal Strings
+
+Strings support common escape sequences from C:
+    "\n", "\t", "\r"
+    "\(octal value)"
+    "\x(hex value)"
+
+
+4.5.6) Identifiers
+
+Identifiers references are resolved using dynamic symbol table
+scoping rules.  An identifier referenced on the right-hand-side
+of an expression must be resolvable or else it is an error.
+
+An identifier occurring on the left-hand-side of a ':=' assignment
+is first sought and used if found.  If it is not found, it is
+introduced dynamically in the innermost, current scope.
+
+Sometimes identifiers can be used without the leading slash,
+other times they are required, especially if to disambiguate
+from property names.  It's not ideal yet at all.
+
+
+4.6) Labels and References
 
 Labels may be applied to nodes or properties.  Labels appear
 before a node name, and are referenced using an ampersand: &label.
@@ -239,6 +637,34 @@ And used in properties, lables may appear before or after any value:
 	...
     };
 
+The names of some labels can be constructed in an expression
+context using the representation "&( <string_expr> )".
+
+
+4.7) Symbol Table
+
+During the execution of the program, the evaluation context for
+both statements and expressions is performed in the context of
+a dynamic scoping environment.  That is, as each function,
+subroutine or for-loop is encountered, a new symbol table scope
+is pushed onto a dynamic run-time stack.  When an identifier's
+name needs to be resolved and a value for it determined, a
+search is performed from the inner-most, current top of the
+scope-stack back through the dynamic scope stack towards the
+outer-most and earliest scope.
+
+At each scope, an attempt is made to locate the symbol.  If it
+is found, that is the symbol that is used.  If the symbol can not
+be found at any level, it may be an error, or it may be cause to
+introduce the symbol, as determined by the context in which the
+identifier occurs.
+
+Constants from the command line using the "-D id=value" construct
+are introduced into the outermost scope prior to beginning to
+execute the source file proper.  This is the same outer-most scope
+into which the /const/ and /define/ function symbols are also
+introduced.
+
 
 
 II - The DT block format
-- 
1.6.0.90.g436ed