Re: [PATCH] cpufreq: make table sentinal macros unsigned to match use

From: Brian W Hart
Date: Fri Jul 11 2014 - 18:06:43 EST


On Mon, Jun 30, 2014 at 10:25:20AM +0530, Viresh Kumar wrote:
> On 28 June 2014 02:39, Brian W Hart <hartb@xxxxxxxxxxxxxxxxxx> wrote:
> > 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 âcpufreq_next_validâ:
> > .../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@xxxxxxxxxxxxxxxxxx>
> > ---
> > 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.
>
> I would have moved some of it to logs, they look good.
>
> > 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)
>
> Thanks.
>
> Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>

I haven't seen this appear in the linux-pm tree yet. Is there anything
further needed on my part--aside from patience?

Thank you,
brian

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