dma-debug: remove DMA_API_DEBUG_SG

The scatterlist validity checks are pretty simple and cheap, perform them
unconditionally.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Author: Christoph Hellwig

kernel/dma/Kconfig

@@ -260,23 +260,6 @@ config DMA_API_DEBUG
 
 	  If unsure, say N.
 
-config DMA_API_DEBUG_SG
-	bool "Debug DMA scatter-gather usage"
-	default y
-	depends on DMA_API_DEBUG
-	help
-	  Perform extra checking that callers of dma_map_sg() have respected the
-	  appropriate segment length/boundary limits for the given device when
-	  preparing DMA scatterlists.
-
-	  This is particularly likely to have been overlooked in cases where the
-	  dma_map_sg() API is used for general bulk mapping of pages rather than
-	  preparing literal scatter-gather descriptors, where there is a risk of
-	  unexpected behaviour from DMA API implementations if the scatterlist
-	  is technically out-of-spec.
-
-	  If unsure, say N.
-
 config DMA_MAP_BENCHMARK
 	bool "Enable benchmarking of streaming DMA mapping"
 	depends on DEBUG_FS

kernel/dma/debug.c

@@ -1163,7 +1163,6 @@ static void check_sync(struct device *dev,
 
 static void check_sg_segment(struct device *dev, struct scatterlist *sg)
 {
-#ifdef CONFIG_DMA_API_DEBUG_SG
 	unsigned int max_seg = dma_get_max_seg_size(dev);
 	u64 start, end, boundary = dma_get_seg_boundary(dev);
 
@@ -1184,7 +1183,6 @@ static void check_sg_segment(struct device *dev, struct scatterlist *sg)
 	if ((start ^ end) & ~boundary)
 		err_printk(dev, NULL, "mapping sg segment across boundary [start=0x%016llx] [end=0x%016llx] [boundary=0x%016llx]\n",
 			   start, end, boundary);
-#endif
 }
 
 void debug_dma_map_single(struct device *dev, const void *addr,