scripts: add Linux .cocciconfig for coccinelle

Coccinelle supports reading .cocciconfig, the order of precedence for
variables for .cocciconfig is as follows:

 o Your current user's home directory is processed first
 o Your directory from which spatch is called is processed next
 o The directory provided with the --dir option is processed last, if used

Since coccicheck runs through make, it naturally runs from the kernel
proper dir, as such the second rule above would be implied for picking up a
.cocciconfig when using 'make coccicheck'.

'make coccicheck' also supports using M= targets.If you do not supply
any M= target, it is assumed you want to target the entire kernel.
The kernel coccicheck script has:

    if [ "$KBUILD_EXTMOD" = "" ] ; then
        OPTIONS="--dir $srctree $COCCIINCLUDE"
    else
        OPTIONS="--dir $KBUILD_EXTMOD $COCCIINCLUDE"
    fi

KBUILD_EXTMOD is set when an explicit target with M= is used. For both cases
the spatch --dir argument is used, as such third rule applies when
...

.cocciconfig

+[spatch]
+	options = --timeout 200
+	options = --use-gitgrep

.gitignore

@@ -66,6 +66,7 @@ Module.symvers
 #
 !.gitignore
 !.mailmap
+!.cocciconfig
 
 #
 # Generated include files

Documentation/coccinelle.txt

@@ -189,6 +189,60 @@ work.
 
 DEBUG_FILE support is only supported when using coccinelle >= 1.2.
 
+ .cocciconfig support
+~~~~~~~~~~~~~~~~~~~~~~
+
+Coccinelle supports reading .cocciconfig for default Coccinelle options that
+should be used every time spatch is spawned, the order of precedence for
+variables for .cocciconfig is as follows:
+
+  o Your current user's home directory is processed first
+  o Your directory from which spatch is called is processed next
+  o The directory provided with the --dir option is processed last, if used
+
+Since coccicheck runs through make, it naturally runs from the kernel
+proper dir, as such the second rule above would be implied for picking up a
+.cocciconfig when using 'make coccicheck'.
+
+'make coccicheck' also supports using M= targets.If you do not supply
+any M= target, it is assumed you want to target the entire kernel.
+The kernel coccicheck script has:
+
+    if [ "$KBUILD_EXTMOD" = "" ] ; then
+        OPTIONS="--dir $srctree $COCCIINCLUDE"
+    else
+        OPTIONS="--dir $KBUILD_EXTMOD $COCCIINCLUDE"
+    fi
+
+KBUILD_EXTMOD is set when an explicit target with M= is used. For both cases
+the spatch --dir argument is used, as such third rule applies when whether M=
+is used or not, and when M= is used the target directory can have its own
+.cocciconfig file. When M= is not passed as an argument to coccicheck the
+target directory is the same as the directory from where spatch was called.
+
+If not using the kernel's coccicheck target, keep the above precedence
+order logic of .cocciconfig reading. If using the kernel's coccicheck target,
+override any of the kernel's .coccicheck's settings using SPFLAGS.
+
+We help Coccinelle when used against Linux with a set of sensible defaults
+options for Linux with our own Linux .cocciconfig. This hints to coccinelle
+git can be used for 'git grep' queries over coccigrep. A timeout of 200
+seconds should suffice for now.
+
+The options picked up by coccinelle when reading a .cocciconfig do not appear
+as arguments to spatch processes running on your system, to confirm what
+options will be used by Coccinelle run:
+
+      spatch --print-options-only
+
+You can override with your own preferred index option by using SPFLAGS. Take
+note that when there are conflicting options Coccinelle takes precedence for
+the last options passed. Using .cocciconfig is possible to use idutils, however
+given the order of precedence followed by Coccinelle, since the kernel now
+carries its own .cocciconfig, you will need to use SPFLAGS to use idutils if
+desired. See below section "Additional flags" for more details on how to use
+idutils.
+
  Additional flags
 ~~~~~~~~~~~~~~~~~~
 
@@ -197,8 +251,24 @@ variable. This works as Coccinelle respects the last flags
 given to it when options are in conflict.
 
     make SPFLAGS=--use-glimpse coccicheck
+
+Coccinelle supports idutils as well but requires coccinelle >= 1.0.6.
+When no ID file is specified coccinelle assumes your ID database file
+is in the file .id-utils.index on the top level of the kernel, coccinelle
+carries a script scripts/idutils_index.sh which creates the database with
+
+    mkid -i C --output .id-utils.index
+
+If you have another database filename you can also just symlink with this
+name.
+
     make SPFLAGS=--use-idutils coccicheck
 
+Alternatively you can specify the database filename explicitly, for
+instance:
+
+    make SPFLAGS="--use-idutils /full-path/to/ID" coccicheck
+
 See spatch --help to learn more about spatch options.
 
 Note that the '--use-glimpse' and '--use-idutils' options