linux-kernel - [PATCH] cpufreq: make table sentinal macros unsigned to match use

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Date:	Fri, 27 Jun 2014 16:09:39 -0500
From:	Brian W Hart <hartb@...ux.vnet.ibm.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-sh@...r.kernel.org,
	Stratos Karafotis <stratosk@...aphore.gr>,
	Simon Horman <horms@...ge.net.au>,
	Magnus Damm <magnus.damm@...il.com>
Subject: [PATCH] cpufreq: make table sentinal macros unsigned to match use

Commit 5eeaf1f18973 (cpufreq: Fix build error on some platforms that
use cpufreq_for_each_*) moved function cpufreq_next_valid() to a public
header.  Warnings are now generated when objects including that header
are built with -Wsign-compare (as an out-of-tree module might be):

.../include/linux/cpufreq.h: In function ‘cpufreq_next_valid’:
.../include/linux/cpufreq.h:519:27: warning: comparison between signed
and unsigned integer expressions [-Wsign-compare]
  while ((*pos)->frequency != CPUFREQ_TABLE_END)
                           ^
.../include/linux/cpufreq.h:520:25: warning: comparison between signed
and unsigned integer expressions [-Wsign-compare]
   if ((*pos)->frequency != CPUFREQ_ENTRY_INVALID)
                         ^

Constants CPUFREQ_ENTRY_INVALID and CPUFREQ_TABLE_END are signed, but
are used with unsigned member 'frequency' of cpufreq_frequency_table.
Update the macro definitions to be explicitly unsigned to match their
use.

This also corrects potentially wrong behavior of clk_rate_table_iter()
if unsigned long is wider than usigned int.

Signed-off-by: Brian W Hart <hartb@...ux.vnet.ibm.com>
---
These macros are fairly broadly used in the kernel so I was bit leery
of changing them, but after inspection I think it's fine.  I found 102
uses of the macros, of which:

99 are uses with cpufreq_frequency_table.frequency (95) or with local
   variables of the same type as frequency (4).  These should be just
   fine with this change--we're just making explicit a conversion that
   was previously implicit.

 2 are uses with a local variable of different type (unsigned long) than
   'frequency' (in drivers/sh/clk/core.c).  One of these uses is safe;
   the other (in clk_rate_table_iter()) is broken if unsigned long
   is wider than unsigned int.  As a side-effect, this patch corrects
   the potential misbehavior there.

 1 is a use in macro cpufreq_for_each_entry() with what _should_ be the
   frequency member of a cpufreq_frequency_table, provided the caller it
   well-behaved.  There are 18 callers of this macro; all are well-behaved.
   So these should also be safe.

 include/linux/cpufreq.h |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index ec4112d..8f8ae95 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -482,8 +482,8 @@ extern struct cpufreq_governor cpufreq_gov_conservative;
  *********************************************************************/

 /* Special Values of .frequency field */
-#define CPUFREQ_ENTRY_INVALID	~0
-#define CPUFREQ_TABLE_END	~1
+#define CPUFREQ_ENTRY_INVALID	~0u
+#define CPUFREQ_TABLE_END	~1u
 /* Special Values of .flags field */
 #define CPUFREQ_BOOST_FREQ	(1 << 0)

-- 
1.7.1

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