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

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Date:   Tue, 23 Jun 2020 11:19:47 +0100
From:   John Garry <john.garry@...wei.com>
To:     Rikard Falkeborn <rikard.falkeborn@...il.com>,
        "joro@...tes.org" <joro@...tes.org>
CC:     kernel test robot <lkp@...el.com>, <will@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "kbuild-all@...ts.01.org" <kbuild-all@...ts.01.org>,
        "trivial@...nel.org" <trivial@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linuxarm <linuxarm@...wei.com>, "maz@...nel.org" <maz@...nel.org>
Subject: Re: [PATCH 4/4] iommu/arm-smmu-v3: Remove cmpxchg() in
 arm_smmu_cmdq_issue_cmdlist()

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