linux-kernel - [PATCH] dma-mapping: avoid potential unused data compilation warning

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Message-Id: <20250415075659.428549-1-m.szyprowski@samsung.com>
Date: Tue, 15 Apr 2025 09:56:59 +0200
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Cc: Marek Szyprowski <m.szyprowski@...sung.com>, Christoph Hellwig
	<hch@....de>, Robin Murphy <robin.murphy@....com>, netdev@...r.kernel.org,
	Jakub Kicinski <kuba@...nel.org>, Andy Shevchenko
	<andriy.shevchenko@...ux.intel.com>
Subject: [PATCH] dma-mapping: avoid potential unused data compilation
 warning

When CONFIG_NEED_DMA_MAP_STATE is not defined, dma-mapping clients might
report unused data compilation warnings for dma_unmap_*() calls
arguments. Redefine macros for those calls to let compiler to notice that
it is okay when the provided arguments are not used.

Reported-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Suggested-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
---
 include/linux/dma-mapping.h | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index b79925b1c433..85ab710ec0e7 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -629,10 +629,14 @@ static inline int dma_mmap_wc(struct device *dev,
 #else
 #define DEFINE_DMA_UNMAP_ADDR(ADDR_NAME)
 #define DEFINE_DMA_UNMAP_LEN(LEN_NAME)
-#define dma_unmap_addr(PTR, ADDR_NAME)           (0)
-#define dma_unmap_addr_set(PTR, ADDR_NAME, VAL)  do { } while (0)
-#define dma_unmap_len(PTR, LEN_NAME)             (0)
-#define dma_unmap_len_set(PTR, LEN_NAME, VAL)    do { } while (0)
+#define dma_unmap_addr(PTR, ADDR_NAME)           \
+	({ typeof(PTR) __p __maybe_unused = PTR; 0; })
+#define dma_unmap_addr_set(PTR, ADDR_NAME, VAL)  \
+	do { typeof(PTR) __p __maybe_unused = PTR; } while (0)
+#define dma_unmap_len(PTR, LEN_NAME)             \
+	({ typeof(PTR) __p __maybe_unused = PTR; 0; })
+#define dma_unmap_len_set(PTR, LEN_NAME, VAL)    \
+	do { typeof(PTR) __p __maybe_unused = PTR; } while (0)
 #endif
 
 #endif /* _LINUX_DMA_MAPPING_H */
-- 
2.34.1