diff options
| author |   Will Deacon <will.deacon@arm.com> | 2018-09-13 14:28:33 +0100 |
|---|---|---|
| committer | Will Deacon <will.deacon@arm.com> | 2018-12-07 17:28:01 +0000 |
| commit | b4f9209bfcd5964551de434342818334ab9c8c7e (patch) | |
| tree | 69578d6a718bb6f9ff0f3f4cad3cecb801a88758 /arch/arm64/include/asm/atomic_ll_sc.h | |
| parent | arm64: Avoid redundant type conversions in xchg() and cmpxchg() (diff) | |
| download | linux-dev-b4f9209bfcd5964551de434342818334ab9c8c7e.tar.xz linux-dev-b4f9209bfcd5964551de434342818334ab9c8c7e.zip | |
arm64: Avoid masking "old" for LSE cmpxchg() implementation
The CAS instructions implicitly access only the relevant bits of the "old"
argument, so there is no need for explicit masking via type-casting as
there is in the LL/SC implementation.
Move the casting into the LL/SC code and remove it altogether for the LSE
implementation.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64/include/asm/atomic_ll_sc.h')
| -rw-r--r-- | arch/arm64/include/asm/atomic_ll_sc.h | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/atomic_ll_sc.h b/arch/arm64/include/asm/atomic_ll_sc.h index f02d3bf7b9e6..b53f70dd6e10 100644 --- a/arch/arm64/include/asm/atomic_ll_sc.h +++ b/arch/arm64/include/asm/atomic_ll_sc.h @@ -257,6 +257,14 @@ __LL_SC_PREFIX(__cmpxchg_case_##name##sz(volatile void *ptr, \ unsigned long tmp; \ u##sz oldval; \ \ + /* \ + * Sub-word sizes require explicit casting so that the compare \ + * part of the cmpxchg doesn't end up interpreting non-zero \ + * upper bits of the register containing "old". \ + */ \ + if (sz < 32) \ + old = (u##sz)old; \ + \ asm volatile( \ " prfm pstl1strm, %[v]\n" \ "1: ld" #acq "xr" #sfx "\t%" #w "[oldval], %[v]\n" \ |