ACPI 6.4, s6.4.2.9 "End Tag":
"This checksum is generated such that adding it to the sum of all the data
bytes will produce a zero sum."
"If the checksum field is zero, the resource data is treated as if the
checksum operation succeeded. Configuration proceeds normally."
To avoid re-computing checksums, if a new resource data elements is
added/removed/modified in a list of resource data elements, the AmlLib
resets the checksum to 0.
This patch also refactors the AmlAppendRdNode() function by getting the
last Resource Data node directly instead of iterating over all the
elements of the list of Resource Data node.
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>
Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com>
AML has a complex grammar, and this makes runtime modifications
on an AML byte stream difficult. A solution is to parse the AML
bytecode and represent it in a tree data structure, henceforth
called the AML tree.
The AML tree is composite in the sense it has the following node
types:
- A 'Root node' that represents the root of the AML tree.
- An 'Object node' that contains the OP Code (AML Encoding).
- A 'Data node' that contains a data buffer.
The Root node contains the Definition block header (ACPI header)
and a Variable Argument list.
The Object node is composed of an array of Fixed Arguments and
a Variable Argument list.
Fixed arguments can be either Object Nodes or Data nodes. Their
placement (index) in the Fixed Argument array is defined by the
AML encoding of the enclosing Object Node.
Variable arguments can be Object nodes or Data nodes.
Following is a depiction of a typical AML tree:
(/) # Root Node
\
|-{(N1)->...} # Variable Argument list, N1 is
\ # an Object Node
\ /-i # Child of fixed argument b
\ /
|- [a][b][c][d] # Fixed Arguments
|- {(e)->(f)->(g)} # Variable Arguments
\
\-h # Child of variable argument e
Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Alexei Fedorov <Alexei.Fedorov@arm.com>
