dma: contiguous: Reserve default CMA heap

The CMA code, in addition to the reserved-memory regions in the device
tree, will also register a default CMA region if the device tree doesn't
provide any, with its size and position coming from either the kernel
command-line or configuration.

Let's register that one for use to create a heap for it.

Reviewed-by: T.J. Mercier <tjmercier@google.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://lore.kernel.org/r/20251013-dma-buf-ecc-heap-v8-4-04ce150ea3d9@kernel.org

kernel/dma/contiguous.c

@@ -242,6 +242,8 @@ void __init dma_contiguous_reserve(phys_addr_t limit)
 	}
 
 	if (selected_size && !dma_contiguous_default_area) {
+		int ret;
+
 		pr_debug("%s: reserving %ld MiB for global area\n", __func__,
 			 (unsigned long)selected_size / SZ_1M);
 
@@ -249,6 +251,10 @@ void __init dma_contiguous_reserve(phys_addr_t limit)
 					    selected_limit,
 					    &dma_contiguous_default_area,
 					    fixed);
+
+		ret = dma_heap_cma_register_heap(dma_contiguous_default_area);
+		if (ret)
+			pr_warn("Couldn't register default CMA heap.");
 	}
 }