Re: [PATCH 4/4] iommu/arm-smmu-v3: Remove cmpxchg() in arm_smmu_cmdq_issue_cmdlist()

[John Garry <john.garry@huawei.com>]

On 23/06/2020 10:35, Rikard Falkeborn wrote:
> 
>     I'd say that GENMASK_INPUT_CHECK() should be able to handle a l=0 and
>     h=unsigned value, so I doubt this warn.
> 
>     Using GENMASK((int)cmdq->q.llq.max_n_shift, 0) resolves it, but it
>     looks
>     like GENMASK_INPUT_CHECK() could be improved.
> 
> 
> Indeed it could, it is fixed in -next.

ok, thanks for the pointer, but I still see this on today's -next with 
this patch:

make W=1 drivers/iommu/arm-smmu-v3.o

In file included from ./include/linux/bits.h:23:0,
                 from ./include/linux/ioport.h:15,
                 from ./include/linux/acpi.h:12,
                 from drivers/iommu/arm-smmu-v3.c:12:
drivers/iommu/arm-smmu-v3.c: In function ‘arm_smmu_cmdq_issue_cmdlist’:
./include/linux/bits.h:27:7: warning: comparison of unsigned expression 
< 0 is always false [-Wtype-limits]
   (l) > (h), 0)))
       ^
./include/linux/build_bug.h:16:62: note: in definition of macro 
‘BUILD_BUG_ON_ZERO’
#define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
                                                              ^
./include/linux/bits.h:40:3: note: in expansion of macro 
‘GENMASK_INPUT_CHECK’
  (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
   ^~~~~~~~~~~~~~~~~~~
drivers/iommu/arm-smmu-v3.c:1404:18: note: in expansion of macro ‘GENMASK’
  u32 prod_mask = GENMASK(cmdq->q.llq.max_n_shift, 0);

That's gcc 7.5.0 .

Cheers,
John