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

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

[Marek Szyprowski]

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@linux.intel.com>
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.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

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

[Andy Shevchenko]

On Tue, Apr 15, 2025 at 09:56:59AM +0200, Marek Szyprowski wrote:
> 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.

Tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

(GCC on default i386_defconfig with `make W=1` on v6.15-rc2)

-- 
With Best Regards,
Andy Shevchenko

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

[Marek Szyprowski]

On 15.04.2025 11:39, Andy Shevchenko wrote:
> On Tue, Apr 15, 2025 at 09:56:59AM +0200, Marek Szyprowski wrote:
>> 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.
> Tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
>
> (GCC on default i386_defconfig with `make W=1` on v6.15-rc2)

Applied to dma-mapping-fixes branch.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland