linux-yocto: warn when a generated BSP description is used

The meta data (in tree or out of tree) that describes a BSP, its patches
and configuration is not always available when a new/default or manually
configured machine is built.

When this happens, the tools generate a skeleton BSP and use a
architecture defconfig for the build. If this is by design, the build
is typically sane and everything works fine. If an existing BSP
description was expected, chances are that the resulting kernel will not
be correct.

To avoid surprising the user when a default/skeleton BSP is used for the
build, we can make it obvious to the user by emitting a warning like
the following:

   WARNING: [kernel]: An auto generated BSP description was used, this normally indicates a misconfiguration.
            Check that your machine (myqemux86-64) has an associated kernel description.

[YOCTO: #3383]

(From OE-Core rev: f4a460afc4e2676cbf1daaa1d6723da9e6146526)

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/kernel-yocto.bbclass

@@ -281,6 +281,15 @@ python do_kernel_configcheck() {
             with open (nonhw_file, "r") as myfile:
                 results = myfile.read()
                 bb.warn( "[kernel config]: BSP specified non-hw configuration:\n\n%s" % results)
+
+    bsp_desc = "${S}/" + kmeta + "/" + "top_tgt"
+    if os.path.exists(bsp_desc):
+        with open (bsp_desc, "r") as myfile:
+                bsp_tgt = myfile.read()
+                m = re.match("^(.*)scratch.obj(.*)$", bsp_tgt)
+                if not m is None:
+                    bb.warn( "[kernel]: An auto generated BSP description was used, this normally indicates a misconfiguration.\n" +
+                             "Check that your machine (%s) has an associated kernel description." % "${MACHINE}" )
 }
 
 # Ensure that the branches (BSP and meta) are on the locations specified by