Re: [PATCH net v3 1/3] rtase: Modify the condition used to detect overflow in rtase_calc_time_mitigation

[Simon Horman <horms@kernel.org>]

On Thu, Apr 17, 2025 at 04:56:57PM +0800, Justin Lai wrote:
> Fix the following compile error reported by the kernel test
> robot by modifying the condition used to detect overflow in
> rtase_calc_time_mitigation.
> 
> In file included from include/linux/mdio.h:10:0,
>                   from drivers/net/ethernet/realtek/rtase/rtase_main.c:58:
>  In function 'u16_encode_bits',
>      inlined from 'rtase_calc_time_mitigation.constprop' at drivers/net/
>      ethernet/realtek/rtase/rtase_main.c:1915:13,
>      inlined from 'rtase_init_software_variable.isra.41' at drivers/net/
>      ethernet/realtek/rtase/rtase_main.c:1961:13,
>      inlined from 'rtase_init_one' at drivers/net/ethernet/realtek/
>      rtase/rtase_main.c:2111:2:
> >> include/linux/bitfield.h:178:3: error: call to '__field_overflow'
>       declared with attribute error: value doesn't fit into mask
>     __field_overflow();     \
>     ^~~~~~~~~~~~~~~~~~
>  include/linux/bitfield.h:198:2: note: in expansion of macro
>  '____MAKE_OP'
>    ____MAKE_OP(u##size,u##size,,)
>    ^~~~~~~~~~~
>  include/linux/bitfield.h:200:1: note: in expansion of macro
>  '__MAKE_OP'
>   __MAKE_OP(16)
>   ^~~~~~~~~
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202503182158.nkAlbJWX-lkp@intel.com/
> Fixes: a36e9f5cfe9e ("rtase: Add support for a pci table in this module")
> Signed-off-by: Justin Lai <justinlai0215@realtek.com>

Hi Justin,

FWIIW, I note that this problem is reported by GCC 7.5.0 on sparc64 but not
by GCC 14.2.0. And I think that is because in the end the values passed to
u16_encode_bits (line 1915 in the trace above) are the same with and
without this patch. That is to say, this the compiler error above is a
false positive of sorts.

But I believe GCC 7.5.0 is a supported compiler version for sparc64.
And this does result in an error, without W=1 or any other extra KCFLAGS
set. So I agree this is appropriate to treat as a fix for net.

And in any case, fix or no fix, it seems nice to limit the scope of
the initialisation of msb.

Reviewed-by: Simon Horman <horms@kernel.org>