dma: contiguous: Make dev_get_cma_area() a proper function

As we try to enable dma-buf heaps, and the CMA one in particular, to
compile as modules, we need to export dev_get_cma_area(). It's currently
implemented as an inline function that returns either the content of
device->cma_area or dma_contiguous_default_area.

Thus, it means we need to export dma_contiguous_default_area, which
isn't really something we want any module to have access to.

Instead, let's make dev_get_cma_area() a proper function we will be able
to export so we can avoid exporting dma_contiguous_default_area.

Signed-off-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20260331-dma-buf-heaps-as-modules-v4-2-e18fda504419@kernel.org

Author: mripard

include/linux/dma-map-ops.h

@@ -93,12 +93,7 @@ static inline void set_dma_ops(struct device *dev,
 #ifdef CONFIG_DMA_CMA
 extern struct cma *dma_contiguous_default_area;
 
-static inline struct cma *dev_get_cma_area(struct device *dev)
-{
-	if (dev && dev->cma_area)
-		return dev->cma_area;
-	return dma_contiguous_default_area;
-}
+struct cma *dev_get_cma_area(struct device *dev);
 struct cma *dma_contiguous_get_area_by_idx(unsigned int idx);
 
 void dma_contiguous_reserve(phys_addr_t addr_limit);

kernel/dma/contiguous.c

@@ -131,6 +131,14 @@ bool __init cma_skip_dt_default_reserved_mem(void)
 	return size_cmdline != -1;
 }
 
+struct cma *dev_get_cma_area(struct device *dev)
+{
+	if (dev && dev->cma_area)
+		return dev->cma_area;
+
+	return dma_contiguous_default_area;
+}
+
 #ifdef CONFIG_DMA_NUMA_CMA
 
 static struct cma *dma_contiguous_numa_area[MAX_NUMNODES];