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

On 23/06/2020 14:55, Rikard Falkeborn wrote:

Den tis 23 juni 2020 12:21John Garry <john.garry@huawei.com 
<mailto:john.garry@huawei.com>> skrev:

    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


Oh, ok thanks for reporting. I guess different gcc versions have 
different behaviour. I guess we'll have to change the comparison to 
(!((h) == (l) || (h) > (l))) instead (not sure I got all parenthesis and 
logic correct but you get the idea).

Yeah, so this looks to fix it:

--- a/include/linux/bits.h
+++ b/include/linux/bits.h

@@ -23,7 +23,8 @@

#include <linux/build_bug.h>
#define GENMASK_INPUT_CHECK(h, l) \
        (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
-               __builtin_constant_p((l) > (h)), (l) > (h), 0)))
+               __builtin_constant_p(!((h) == (l) ||(h) > (l))), !((h) 
== (l) ||(h) > (l)), 0)))
+

We may be able to just use (h) == (l) as the const expr to make it more 
concise, but that may be confusing.

I only tested with my toolchain based on 7.5.0

Thanks,
John


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