[PATCH] m68k: hash: Use lower_16_bits() helper

[Geert Uytterhoeven]

When building for m68k with CONFIG_M68000=y and C=1:

    drivers/clk/rockchip/clk-rk3528.c: note: in included file (through include/linux/hash.h, include/linux/slab.h):
    arch/m68k/include/asm/hash.h:57:24: warning: cast truncates bits from constant value (18720 becomes 8720)
    arch/m68k/include/asm/hash.h:57:24: warning: cast truncates bits from constant value (1e8e8 becomes e8e8)

Sparse does not realize the truncation is intentional.
Make this explicit by using the lower_16_bits() helper instead, which
also masks the unwanted bits.

Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202605191434.PQkj2Rki-lkp@xxxxxxxxx/
Reported-by: Heiko Stuebner <heiko@xxxxxxxxx>
Closes: https://lore.kernel.org/20260603213726.1025094-1-heiko@xxxxxxxxx/
Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
---
No change in generated code.

 arch/m68k/include/asm/hash.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/m68k/include/asm/hash.h b/arch/m68k/include/asm/hash.h
index 6d0d0c893f16dd49..6dadf493706632f5 100644
--- a/arch/m68k/include/asm/hash.h
+++ b/arch/m68k/include/asm/hash.h
@@ -2,6 +2,8 @@
 #ifndef _ASM_HASH_H
 #define _ASM_HASH_H
 
+#include <linux/wordpart.h>
+
 /*
  * If CONFIG_M68000=y (original mc68000/010), this file is #included
  * to work around the lack of a MULU.L instruction.
@@ -54,7 +56,7 @@ static inline u32 __attribute_const__ __hash_32(u32 x)
 	: "=&d,d" (a), "=&r,r" (b)
 	: "r,roi?" (x));	/* a+b = x*0x8647 */
 
-	return ((u16)(x*0x61c8) << 16) + a + b;
+	return (lower_16_bits(x * 0x61c8) << 16) + a + b;
 }
 
 #endif	/* _ASM_HASH_H */
-- 
2.43.0