kernel/dtm: Add an example on the kernel DT API

This comes in the form of a simple kernel module which iterates over
CPUs and prints the contents of some device tree nodes.

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/kernel/dtm/README.md b/kernel/dtm/README.md
new file mode 100644
index 0000000..593c1d2
--- /dev/null
+++ b/kernel/dtm/README.md
@@ -0,0 +1,29 @@
+# Device Tree Module
+
+This is a simple kernel module which show cases some of the kernel API functions
+for manipulating device tree nodes.
+
+In order to build this module you need either a local build of the Linux kernel,
+or the the source that you can get from your Linux distribution (e.g.
+`kernel-source` on openSUSE). For the former you will need to specify the path
+to your local development tree with the `KERNEL` variable. So:
+
+```
+$ make KERNEL=<path/to/development/tree>
+```
+
+This will produce a `dtm.ko` file, which you will need to `insmod` on your
+target machine. Then you will get this output from `dmesg`:
+
+```
+[  571.298548] [    T813] dtm: loading out-of-tree module taints kernel.
+[  571.305842] [    T813] Inside of VisionFive2
+[  571.309945] [    T813] RISC-V ISA for 'cpu@1': rv64imafdc_zba_zbb
+[  571.315826] [    T813] parent: cpus
+[  571.319091] [    T813] RISC-V ISA for 'cpu@2': rv64imafdc_zba_zbb
+[  571.324962] [    T813] parent: cpus
+[  571.328224] [    T813] RISC-V ISA for 'cpu@3': rv64imafdc_zba_zbb
+[  571.334092] [    T813] parent: cpus
+[  571.337354] [    T813] RISC-V ISA for 'cpu@4': rv64imafdc_zba_zbb
+[  571.343228] [    T813] parent: cpus
+```