On 11/05/2021 13:35, Nathan Chancellor wrote: > On Tue, May 11, 2021 at 07:00:34PM +0300, Dmitry Osipenko wrote: >> 11.05.2021 18:31, Krzysztof Kozlowski пишет: >> ... >> ~~~~~~~~~~~~~~~~~~~~~^ >>>>>>> drivers/memory/tegra/tegra124-emc.c:802:26: warning: implicit conversion from 'unsigned long' to 'u32' (aka 'unsigned int') changes value from 18446744071562067985 to 2147483665 [-Wconstant-conversion] >>>>> emc_ccfifo_writel(emc, EMC_ZQ_CAL_LONG_CMD_DEV0, EMC_ZQ_CAL); >>>>> ~~~~~~~~~~~~~~~~~ ^~~~~~~~~~~~~~~~~~~~~~~~ >>>>> drivers/memory/tegra/tegra124-emc.c:154:36: note: expanded from macro 'EMC_ZQ_CAL_LONG_CMD_DEV0' >>>>> (DRAM_DEV_SEL_0 | EMC_ZQ_CAL_LONG | EMC_ZQ_CAL_CMD) >>>>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~ >>>>> 13 warnings generated. >>>> >>>> This doesn't look like a useful warning from clang, it should see that >>>> the constant value itself isn't truncated, hence it should be a problem >>>> of clang. Do you think it's okay to ignore this nonsense? >>> >>> I admit I also do not see the real issue here. The DRAM_DEV_SEL_0 fits >>> in u32 and there is no other bitwise arithmetic than just OR, so why >>> clang assumes it can have 32 most signifcant bits toggled on? >>> >>> +Cc Nathan and Nick, >>> Maybe you could shed some light here on this warning? >>> >>> Dmitry, >>> In general you should not ignore it because: >>> 1. This breaks allyesconfig with clang on powerpc (or it is one of the >>> stoppers), >>> 2. We might want in some future to build it with clang. >> >> I meant to ignore it from the perspective of the memory drivers, i.e. it >> likely should be fixed in clang and not worked around in the code. Thank >> you for pinging the right people. > > I do not think this is a bug in clang, gcc warns the same (just not here > in this case): https://godbolt.org/z/e9GWobMnd > > DRAM_DEV_SEL_0 and DRAM_DEV_SEL_1 are implicitly signed integers because > there is no suffix on the literal 1. DRAM_DEV_SEL_0 is 2 << 30, which > can be turned into 1 << 31. That is equal to INT_MAX + 1, which then > overflows and becomes INT_MIN (undefined behavior). INT_MIN is then > promoted to unsigned long because EMC_ZQ_CAL_LONG and EMC_ZQ_CAL_CMD are > unsigned long due to the BIT macro, resulting in the gigantic number > that clang reports above. > Thanks, good point. Best regards, Krzysztof
