From: Arnd Bergmann
> Sent: 23 March 2021 13:20
> Passing an 8-bit constant into delay() triggers a warning when building
> with 'make W=1' using clang:
>
> drivers/clk/actions/owl-pll.c:182:2: error: result of comparison of constant
> 2000 with expression of
> type 'u8' (aka 'unsigned char') is always false
> [-Werror,-Wtautological-constant-out-of-range-compare]
> udelay(pll_hw->delay);
> ^~~~~~~~~~~~~~~~~~~~~
> arch/arm/include/asm/delay.h:84:9: note: expanded from macro 'udelay'
> ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() : \
> ~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~
> arch/arm/mach-omap2/wd_timer.c:89:3: error: result of comparison of constant
> 2000 with expression of
> type 'u8' (aka 'unsigned char') is always false
> [-Werror,-Wtautological-constant-out-of-range-compare]
> udelay(oh->class->sysc->srst_udelay);
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Shut up the warning by adding a cast to a 64-bit number. A cast to 'int'
> would usually be sufficient, but would fail to cause a link-time error
> for large 64-bit constants.
Adding 0u probably has the desired effect - without any side effects of a cast.
David
>
> Signed-off-by: Arnd Bergmann <a...@arndb.de>
> ---
> arch/arm/include/asm/delay.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm/include/asm/delay.h b/arch/arm/include/asm/delay.h
> index 4f80b72372b4..1bb6417a3a83 100644
> --- a/arch/arm/include/asm/delay.h
> +++ b/arch/arm/include/asm/delay.h
> @@ -81,7 +81,7 @@ extern void __bad_udelay(void);
>
> #define udelay(n) \
> (__builtin_constant_p(n) ? \
> - ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() : \
> + ((u64)(n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() : \
> __const_udelay((n) * UDELAY_MULT)) : \
> __udelay(n))
>
> --
> 2.29.2
-
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