checkpatch: suggest using min_t or max_t

A common issue with min() or max() is using a cast on one or both of the
arguments when using min_t/max_t could be better.

Add cast detection to uses of min/max and suggest an appropriate use of
min_t or max_t instead.

Caveat:  This only works for min() or max() on a single line.
         It does not find min() or max() split across multiple lines.

This does find:
	min((u32)foo, bar);
But it does not find:
	max((unsigned long)foo,
	    bar);

Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index b0aa2c68059..5ba62d8b5e5 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -268,6 +268,20 @@ sub build_types {
 }
 build_types();
 
+our $match_balanced_parentheses = qr/(\((?:[^\(\)]+|(-1))*\))/;
+
+our $Typecast   = qr{\s*(\(\s*$NonptrType\s*\)){0,1}\s*};
+our $LvalOrFunc = qr{($Lval)\s*($match_balanced_parentheses{0,1})\s*};
+
+sub deparenthesize {
+        my ($string) = @_;
+        return "" if (!defined($string));
+        $string =~ s@^\s*\(\s*@@g;
+        $string =~ s@\s*\)\s*$@@g;
+        $string =~ s@\s+@ @g;
+        return $string;
+}
+
 $chk_signoff = 0 if ($file);
 
 my @dep_includes = ();
@@ -2290,6 +2304,27 @@ sub process {
                         }
                 }
 
+# typecasts on min/max could be min_t/max_t
+                if ($line =~ /^\+(?:.*?)\b(min|max)\s*\($Typecast{0,1}($LvalOrFunc)\s*,\s*$Typecast{0,1}($LvalOrFunc)\s*\)/) {
+                        if (defined $2 || defined $8) {
+                                my $call = $1;
+                                my $cast1 = deparenthesize($2);
+                                my $arg1 = $3;
+                                my $cast2 = deparenthesize($8);
+                                my $arg2 = $9;
+                                my $cast;
+
+                                if ($cast1 ne "" && $cast2 ne "") {
+                                        $cast = "$cast1 or $cast2";
+                                } elsif ($cast1 ne "") {
+                                        $cast = $cast1;
+                                } else {
+                                        $cast = $cast2;
+                                }
+                                WARN("$call() should probably be ${call}_t($cast, $arg1, $arg2)\n" . $herecurr);
+                        }
+                }
+
 # Need a space before open parenthesis after if, while etc
                 if ($line=~/\b(if|while|for|switch)\(/) {
                         ERROR("space required before the open parenthesis '('\n" . $herecurr);