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SubjectRe: [PATCH 05/21] powerpc: Avoid comparison of unsigned long >= 0 in pfn_valid
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Mathieu Malaterre <malat@debian.org> writes:

> Rewrite comparison since all values compared are of type `unsigned long`.
>
> Fix a warning (treated as error in W=1):
>
> CC arch/powerpc/kernel/irq.o
> In file included from ./include/linux/bug.h:5:0,
> from ./include/linux/cpumask.h:13,
> from ./include/linux/smp.h:13,
> from ./include/linux/kernel_stat.h:5,
> from arch/powerpc/kernel/irq.c:35:
> ./include/linux/dma-mapping.h: In function ‘dma_map_resource’:
> ./arch/powerpc/include/asm/page.h:129:32: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
> #define pfn_valid(pfn) ((pfn) >= ARCH_PFN_OFFSET && (pfn) < max_mapnr)
> ^
> Suggested-by: Segher Boessenkool <segher@kernel.crashing.org>
> Signed-off-by: Mathieu Malaterre <malat@debian.org>
> ---
> arch/powerpc/include/asm/page.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
> index 8da5d4c1cab2..19dea64e7ed2 100644
> --- a/arch/powerpc/include/asm/page.h
> +++ b/arch/powerpc/include/asm/page.h
> @@ -126,7 +126,8 @@ extern long long virt_phys_offset;
>
> #ifdef CONFIG_FLATMEM
> #define ARCH_PFN_OFFSET ((unsigned long)(MEMORY_START >> PAGE_SHIFT))
> -#define pfn_valid(pfn) ((pfn) >= ARCH_PFN_OFFSET && (pfn) < max_mapnr)
> +#define pfn_valid(pfn) \
> + (((pfn) - ARCH_PFN_OFFSET) < (max_mapnr - ARCH_PFN_OFFSET))

I'm not a big fan of this one, because the original code is *far* more
obvious as to what it's doing.

I'm not sure if we can make this one a static inline, or whether that
would help, but it would be worth investigating.

cheers

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