fit: Support compat string property in configuration node

This patch adds support for an optional optimization to compatible
string matching where the compatible string property from the root node
of the kernel FDT can be copied into the configuration node of the FIT
image. This is most useful when using compressed FDTs or when using FDT
overlays, where the traditional extraction of the compatible string from
the kernel FDT itself is not easily possible.

Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>

2 files changed, 80 insertions, 0 deletions

diff --git a/doc/uImage.FIT/kernel_fdts_compressed.its b/doc/uImage.FIT/kernel_fdts_compressed.its
new file mode 100644
index 0000000000..8f81106efc
--- /dev/null
+++ b/doc/uImage.FIT/kernel_fdts_compressed.its
@@ -0,0 +1,73 @@
+/*
+ * U-Boot uImage source file with a kernel and multiple compressed FDT blobs.
+ * Since the FDTs are compressed, configurations must provide a compatible
+ * string to match directly.
+ */
+
+/dts-v1/;
+
+/ {
+	description = "Image with single Linux kernel and compressed FDT blobs";
+	#address-cells = <1>;
+
+	images {
+		kernel {
+			description = "Vanilla Linux kernel";
+			data = /incbin/("./vmlinux.bin.gz");
+			type = "kernel";
+			arch = "ppc";
+			os = "linux";
+			compression = "gzip";
+			load = <00000000>;
+			entry = <00000000>;
+			hash-1 {
+				algo = "crc32";
+			};
+			hash-2 {
+				algo = "sha1";
+			};
+		};
+		fdt@1 {
+			description = "Flattened Device Tree blob 1";
+			data = /incbin/("./myboard-var1.dtb");
+			type = "flat_dt";
+			arch = "ppc";
+			compression = "gzip";
+			hash-1 {
+				algo = "crc32";
+			};
+			hash-2 {
+				algo = "sha1";
+			};
+		};
+		fdt@2 {
+			description = "Flattened Device Tree blob 2";
+			data = /incbin/("./myboard-var2.dtb");
+			type = "flat_dt";
+			arch = "ppc";
+			compression = "lzma";
+			hash-1 {
+				algo = "crc32";
+			};
+			hash-2 {
+				algo = "sha1";
+			};
+		};
+	};
+
+	configurations {
+		default = "conf@1";
+		conf@1 {
+			description = "Boot Linux kernel with FDT blob 1";
+			kernel = "kernel";
+			fdt = "fdt@1";
+			compatible = "myvendor,myboard-variant1";
+		};
+		conf@2 {
+			description = "Boot Linux kernel with FDT blob 2";
+			kernel = "kernel";
+			fdt = "fdt@2";
+			compatible = "myvendor,myboard-variant2";
+		};
+	};
+};
diff --git a/doc/uImage.FIT/source_file_format.txt b/doc/uImage.FIT/source_file_format.txt
index d701b9bb76..f8e27ed34e 100644
--- a/doc/uImage.FIT/source_file_format.txt
+++ b/doc/uImage.FIT/source_file_format.txt
@@ -240,6 +240,7 @@ o config-1
   |- fdt = "fdt sub-node unit-name" [, "fdt overlay sub-node unit-name", ...]
   |- fpga = "fpga sub-node unit-name"
   |- loadables = "loadables sub-node unit-name"
+  |- compatible = "vendor,board-style device tree compatible string"
 
 
   Mandatory properties:
@@ -263,6 +264,12 @@ o config-1
     of strings. U-Boot will load each binary at its given start-address and
     may optionaly invoke additional post-processing steps on this binary based
     on its component image node type.
+  - compatible : The root compatible string of the U-Boot device tree that
+    this configuration shall automatically match when CONFIG_FIT_BEST_MATCH is
+    enabled. If this property is not provided, the compatible string will be
+    extracted from the fdt blob instead. This is only possible if the fdt is
+    not compressed, so images with compressed fdts that want to use compatible
+    string matching must always provide this property.
 
 The FDT blob is required to properly boot FDT based kernel, so the minimal
 configuration for 2.6 FDT kernel is (kernel, fdt) pair.