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SubjectRe: [PATCH] cpufreq: make table sentinal macros unsigned to match use
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On 28 June 2014 02:39, Brian W Hart <hartb@linux.vnet.ibm.com> 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 ‘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@linux.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.

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@linaro.org>
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