Merge tag 'dma-mapping-6.15-2025-04-25' of git://git.kernel.org/pub/scm/linux/kernel/git/mszyprowski/linux

Pull dma-maping fixes from Marek Szyprowski:

 - avoid unused variable warnings (Arnd Bergmann, Marek Szyprowski)

 - add runtume warnings and debug messages for devices with limited DMA
   capabilities (Balbir Singh, Chen-Yu Tsai)

* tag 'dma-mapping-6.15-2025-04-25' of git://git.kernel.org/pub/scm/linux/kernel/git/mszyprowski/linux:
  dma-coherent: Warn if OF reserved memory is beyond current coherent DMA mask
  dma-mapping: Fix warning reported for missing prototype
  dma-mapping: avoid potential unused data compilation warning
  dma/mapping.c: dev_dbg support for dma_addressing_limited
  dma/contiguous: avoid warning about unused size_bytes

Author: torvalds

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 */

kernel/dma/coherent.c

@@ -336,16 +336,22 @@ static phys_addr_t dma_reserved_default_memory_size __initdata;
 
 static int rmem_dma_device_init(struct reserved_mem *rmem, struct device *dev)
 {
-	if (!rmem->priv) {
-		struct dma_coherent_mem *mem;
+	struct dma_coherent_mem *mem = rmem->priv;
 
+	if (!mem) {
 		mem = dma_init_coherent_memory(rmem->base, rmem->base,
 					       rmem->size, true);
 		if (IS_ERR(mem))
 			return PTR_ERR(mem);
 		rmem->priv = mem;
 	}
-	dma_assign_coherent_memory(dev, rmem->priv);
+
+	/* Warn if the device potentially can't use the reserved memory */
+	if (mem->device_base + rmem->size - 1 >
+	    min_not_zero(dev->coherent_dma_mask, dev->bus_dma_limit))
+		dev_warn(dev, "reserved memory is beyond device's set DMA address range\n");
+
+	dma_assign_coherent_memory(dev, mem);
 	return 0;
 }
 

kernel/dma/contiguous.c

@@ -64,8 +64,7 @@ struct cma *dma_contiguous_default_area;
  * Users, who want to set the size of global CMA area for their system
  * should use cma= kernel parameter.
  */
-static const phys_addr_t size_bytes __initconst =
-	(phys_addr_t)CMA_SIZE_MBYTES * SZ_1M;
+#define size_bytes ((phys_addr_t)CMA_SIZE_MBYTES * SZ_1M)
 static phys_addr_t  size_cmdline __initdata = -1;
 static phys_addr_t base_cmdline __initdata;
 static phys_addr_t limit_cmdline __initdata;

kernel/dma/mapping.c

@@ -910,6 +910,19 @@ int dma_set_coherent_mask(struct device *dev, u64 mask)
 }
 EXPORT_SYMBOL(dma_set_coherent_mask);
 
+static bool __dma_addressing_limited(struct device *dev)
+{
+	const struct dma_map_ops *ops = get_dma_ops(dev);
+
+	if (min_not_zero(dma_get_mask(dev), dev->bus_dma_limit) <
+			 dma_get_required_mask(dev))
+		return true;
+
+	if (unlikely(ops) || use_dma_iommu(dev))
+		return false;
+	return !dma_direct_all_ram_mapped(dev);
+}
+
 /**
  * dma_addressing_limited - return if the device is addressing limited
  * @dev:	device to check
@@ -920,15 +933,11 @@ EXPORT_SYMBOL(dma_set_coherent_mask);
  */
 bool dma_addressing_limited(struct device *dev)
 {
-	const struct dma_map_ops *ops = get_dma_ops(dev);
-
-	if (min_not_zero(dma_get_mask(dev), dev->bus_dma_limit) <
-			 dma_get_required_mask(dev))
-		return true;
-
-	if (unlikely(ops) || use_dma_iommu(dev))
+	if (!__dma_addressing_limited(dev))
 		return false;
-	return !dma_direct_all_ram_mapped(dev);
+
+	dev_dbg(dev, "device is DMA addressing limited\n");
+	return true;
 }
 EXPORT_SYMBOL_GPL(dma_addressing_limited);