checkpatch: allow shorter config descriptions

The requirement of at least 4 line long description for all config
items is often excessive. Add a command line option to control the
required minimum length.

This change to checkpatch has been posted at:
  https://patchwork.kernel.org/patch/4835771/

BUG=None
TEST=prepared a patch with a two line config item description verified
    that by default the insufficient description length warning is
    generated, but when invoked with the new command line option
    (--min-conf-desc-length=2) the patch passes the check.

Change-Id: I477e26d705bccc1b486a3255f22b2abc0cd777ca
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/215730
Reviewed-by: Doug Anderson <dianders@chromium.org>
Commit-Queue: Doug Anderson <dianders@chromium.org>
diff --git a/checkpatch.pl b/checkpatch.pl
index b954de5..c2c9b21 100755
--- a/checkpatch.pl
+++ b/checkpatch.pl
@@ -34,6 +34,7 @@
 my $help = 0;
 my $configuration_file = ".checkpatch.conf";
 my $max_line_length = 80;
+my $min_conf_desc_length = 4;
 
 sub help {
 	my ($exitcode) = @_;
@@ -53,6 +54,7 @@
   --subjective, --strict     enable more subjective tests
   --ignore TYPE(,TYPE2...)   ignore various comma separated message types
   --max-line-length=n        set the maximum line length, if exceeded, warn
+  --min-conf-desc-length=n   set the min description length, if shorter, warn
   --show-types               show the message "types" in the output
   --root=PATH                PATH to the kernel tree root
   --no-summary               suppress the per-file summary
@@ -110,6 +112,7 @@
 	'ignore=s'	=> \@ignore,
 	'show-types!'	=> \$show_types,
 	'max-line-length=i' => \$max_line_length,
+	'min-conf-desc-length=i' => \$min_conf_desc_length,
 	'root=s'	=> \$root,
 	'summary!'	=> \$summary,
 	'mailback!'	=> \$mailback,
@@ -1750,7 +1753,8 @@
 				$length++;
 			}
 			WARN("CONFIG_DESCRIPTION",
-			     "please write a paragraph that describes the config symbol fully\n" . $herecurr) if ($is_start && $is_end && $length < 4);
+			     "please write a paragraph that describes the config symbol fully\n" . $herecurr)
+			    if ($is_start && $is_end && $length < $min_conf_desc_length);
 			#print "is_start<$is_start> is_end<$is_end> length<$length>\n";
 		}