This is missing at present and the fdtget tool is no-longer trivial. Add
a little bit of information.
This might be useful for distributions which want to provide a man page.
Signed-off-by: Simon Glass <sjg@xxxxxxxxxxxx>
---
Documentation/manual.txt | 67 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 67 insertions(+)
diff --git a/Documentation/manual.txt b/Documentation/manual.txt
index 72403ac..dd4d888 100644
--- a/Documentation/manual.txt
+++ b/Documentation/manual.txt
@@ -693,3 +693,70 @@ Where options are:
-i, --input Input base DT blob
-o, --output Output DT blob
-v, --verbose Verbose message output
+
+4 ) fdtget -- Read properties from device tree
+
+This command can be used to obtain individual values from the device tree in a
+nicely formatted way. You can specify multiple nodes to display (when using -p)
+or multiple node/property pairs (when not using -p). For the latter, each
+property is displayed on its own line, with a space between each cell within
+the property.
+
+The syntax of the fdtget command is:
+
+ fdtget <options> <dt file> [<node> <property>]...
+ fdtget -p <options> <dt file> [<node> ]...
+
+where options are:
+
+ <type> s=string, i=int, u=unsigned, x=hex
+ Optional modifier prefix:
+ hh or b=byte, h=2 byte, l=4 byte (default)
+
+ -t, --type <arg> Type of data
+ -p, --properties List properties for each node
+ -l, --list List subnodes for each node
+ -d, --default <arg> Default value to display when the property is missing
+ -P, --decode-phandles Decode phandles to show the target node and (with -c) args (this only supports some common cases)
+ -c, --cells <arg> Cells property in phandle target (e.g. 'gpio' for '#gpio-cells')
+ -h, --help Print this help and exit
+ -V, --version Print version and exit
+
+If -t is not provided, fdtget will try to figure out the type, trying to detect
+strings, string lists and the size of each value in the property. This is
+similar to how fdtdump works, and uses the same heuristics.
+
+The phandle feature (-P) provides a way to decode and display phandles. It
+should only be used on properties which use a particular (fairly common)
+phandle format:
+
+ <phandle> <n cells of stuff> <phandle> <m cells of stuff>
+
+For example, consider this device-tree fragment:
+
+ pinctrl {
+ gpio0: gpio0@ff750000 {
+ #gpio-cells = <2>;
+ };
+ };
+
+ gpio-keys {
+ button@0 {
+ gpios = <&gpio0 5 GPIO_ACTIVE_LOW>;
+ };
+ };
+
+
+Normally fdtget weil display the 'gpios' property like this:
+
+ $ fdtget firefly-rk3288/u-boot.dtb /gpio-keys/button@0 gpios
+ 112 5 1
+
+but with -P was can request that the phandle be decoded and shown as a part:
+
+ $ fdtget firefly-rk3288/u-boot.dtb -P -c gpio /gpio-keys/button@0 gpios
+ /pinctrl/gpio0@ff750000 5 1
+
+Note that '-c gpio' is needed to tell fdtget to use the #gpio-cells property
+to figure out the number of arguments for each phandle. Without that it cannot
+display the arguments correctly.
--
2.17.0.441.gb46fe60e1d-goog
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