Re: [PATCH] parisc: avoid a warning on u8 cast for cmpxchg on u8 pointers

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On 4/6/21 6:59 AM, Gao Xiang wrote:
From: Gao Xiang <hsiangkao@xxxxxxxxxx>

commit b344d6a83d01 ("parisc: add support for cmpxchg on u8 pointers")
can generate a sparse warningi ("cast truncates bits from constant
value"), which has been reported several times [1] [2] [3].

The original code worked as expected, but anyway, let silence such
sparse warning as what others did [4].

[1] https://lore.kernel.org/r/202104061220.nRMBwCXw-lkp@xxxxxxxxx
[2] https://lore.kernel.org/r/202012291914.T5Agcn99-lkp@xxxxxxxxx
[3] https://lore.kernel.org/r/202008210829.KVwn7Xeh%25lkp@xxxxxxxxx
[4] https://lore.kernel.org/r/20210315131512.133720-2-jacopo+renesas@xxxxxxxxxx
Cc: Liam Beguin <liambeguin@xxxxxxxxx>
Cc: Helge Deller <deller@xxxxxx>
Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxx>

applied to the parisc for-next git tree.
(I fixed up the typo above too)

Thanks!
Helge

---
  arch/parisc/include/asm/cmpxchg.h | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/parisc/include/asm/cmpxchg.h b/arch/parisc/include/asm/cmpxchg.h
index cf5ee9b0b393..84ee232278a6 100644
--- a/arch/parisc/include/asm/cmpxchg.h
+++ b/arch/parisc/include/asm/cmpxchg.h
@@ -72,7 +72,7 @@ __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new_, int size)
  #endif
  	case 4: return __cmpxchg_u32((unsigned int *)ptr,
  				     (unsigned int)old, (unsigned int)new_);
-	case 1: return __cmpxchg_u8((u8 *)ptr, (u8)old, (u8)new_);
+	case 1: return __cmpxchg_u8((u8 *)ptr, old & 0xff, new_ & 0xff);
  	}
  	__cmpxchg_called_with_bad_pointer();
  	return old;






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