| Message ID | 20210323132031.2858996-1-arnd@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | ARM: delay: avoid clang -Wtautological-constant warning | expand |
On Tue, Mar 23, 2021 at 02:20:23PM +0100, Arnd Bergmann wrote: > From: Arnd Bergmann <arnd@arndb.de> > > 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. What effect (if any) does this have on code generation when the argument is not constant?
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 <arnd@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 - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
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))