Rework J1939 and ISO TP feature enablingjellyfish_9.99.4jellyfish_9.99.3jellyfish/9.99.4jellyfish/9.99.39.99.49.99.3

Rework the J1939 and ISO TP feature enabling logic in config.cmake to:
- define WITH_FEATURE_J1939 and WITH_FEATURE_ISOTP to default to off,
  thus requiring explicit enabling.  This is safer than making
  assumptions based solely on the presence of the headers at build
  time.
- honor WITH_FEATURE_* definitions given on the cmake command-line;
  the checks for header presence only over-ride an "ON" value if the
  required header is not present.

Bug-AGL: SPEC-3538

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: Ie2b84ac50bbed0bbb775cae49f7f4fbe14f2f8ae

2 files changed, 10 insertions, 1 deletions

diff --git a/docs/3-Installation-J1939.md b/docs/3-Installation-J1939.md
index 8098d47f..71595e41 100644
--- a/docs/3-Installation-J1939.md
+++ b/docs/3-Installation-J1939.md
@@ -79,3 +79,7 @@ cp include/uapi/linux/can.h /usr/include/linux/can.h
 cp include/uapi/linux/can/j1939.h /usr/include/linux/can/
 ```
 
+## Enable support at build time
+
+To enable J1939 support, the binding must be built with -DWITH_FEATURE_J1939=ON.
+If using the autobuild script, add CONFIGURE_ARGS="-DWITH_FEATURE_J1939=ON" to the command used.
diff --git a/docs/4-Installation-ISOTP.md b/docs/4-Installation-ISOTP.md
index c8fc31f6..32a767bb 100644
--- a/docs/4-Installation-ISOTP.md
+++ b/docs/4-Installation-ISOTP.md
@@ -47,4 +47,9 @@ sudo insmod ./net/can/can-isotp.ko
 
 ```bash
 sudo cp include/uapi/linux/can/isotp.h /usr/include/linux/can/
-```
\ No newline at end of file
+```
+
+## Enable support at build time
+
+To enable ISO TP support, the binding must be built with -DWITH_FEATURE_ISOTP=ON.
+If using the autobuild script, add CONFIGURE_ARGS="-DWITH_FEATURE_ISOTP=ON" to the command used.