Clang has a rather annoying behavior of checking for integer
arithmetic problems in code paths that are discarded by gcc
before that perfoms the same checks.
For DMA_BIT_MASK(64), this leads to a warning despite the
result of the macro being completely sensible:
arch/arm/plat-iop/adma.c:146:24: error: shift count >= width of type
[-Werror,-Wshift-count-overflow]
.coherent_dma_mask = DMA_BIT_MASK(64),
The best workaround I could come up with is to shift the
value twice, which makes the macro way less readable but
always has the same result.
Link: https://bugs.llvm.org/show_bug.cgi?id=38789
Reviewed-by: Geert Uytterhoeven
Reviewed-by: Robin Murphy
Signed-off-by: Arnd Bergmann
---
v3: use (2ull << n-1) instead of ((1ull << n-1) << 1)
special-case 0 instead of 64
v2: fix off-by-one error
---
include/linux/dma-mapping.h | 6 +-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 75e60be91e5f..5788d60c2223 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -138,7 +138,11 @@ struct dma_map_ops {
extern const struct dma_map_ops dma_virt_ops;
extern const struct dma_map_ops dma_dummy_ops;
-#define DMA_BIT_MASK(n)(((n) == 64) ? ~0ULL : ((1ULL<<(n))-1))
+/*
+ * Shifting '2' instead of '1' because of
+ * https://bugs.llvm.org/show_bug.cgi?id=38789
+ */
+#define DMA_BIT_MASK(n)(((n) == 0) ? 0ULL : (2ULL<<((n)-1))-1)
#define DMA_MASK_NONE 0x0ULL
--
2.20.0
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