dma-buf: heaps: cma: Create CMA heap for each CMA reserved region

Aside from the main CMA region, it can be useful to allow userspace to
allocate from the other CMA reserved regions.

Indeed, those regions can have specific properties that can be useful to
a specific us-case.

For example, one of them platform I've been with has ECC enabled on the
entire memory but for a specific region. Using that region to allocate
framebuffers can be particular beneficial because enabling the ECC has a
performance and memory footprint cost.

Thus, exposing these regions as heaps user-space can allocate from and
import wherever needed allows to cover that use-case.

For now, only shared-dma-pools regions with the reusable property (ie,
backed by CMA) are supported, but eventually we'll want to support other
DMA pools types.

Since we collected all the CMA regions created during boot, we can
simply iterate over all of them to create the heaps.

This has a weird interaction with the recent work on the CMA name, in
particular the backward compatibility code created by commit
854acbe75f ("dma-buf: heaps: Give default CMA heap a fixed name").

Indeed, the old name was either 'reserved', or the name of the
reserved-memory region device tree node if the linux,cma-default
property was set.

In both these cases, we have now collected this region during boot, and
we're using the same name. So we're now largely redundant with the
code to handle backward compatibility code, and we can thus remove it
and the associated Kconfig option.

Reviewed-by: T.J. Mercier <tjmercier@google.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
   [sumits: rebased the doc to latest]
Link: https://lore.kernel.org/r/20251013-dma-buf-ecc-heap-v8-5-04ce150ea3d9@kernel.org

Documentation/userspace-api/dma-buf-heaps.rst

@@ -24,9 +24,12 @@ following heaps:
    ``CMA_SIZE_MBYTES`` or ``CMA_SIZE_PERCENTAGE`` Kconfig options. Prior
    to Linux 6.17, its name wasn't stable and could be called
    ``reserved``, ``linux,cma``, or ``default-pool``, depending on the
-   platform. From Linux 6.17 onwards, the creation of these heaps is
-   controlled through the ``DMABUF_HEAPS_CMA_LEGACY`` Kconfig option for
-   backwards compatibility.
+   platform.
+
+ - A heap will be created for each reusable region in the device tree
+   with the ``shared-dma-pool`` compatible, using the full device tree
+   node name as its name. The buffer semantics are identical to
+   ``default-cma-region``.
 
 Naming Convention
 =================

drivers/dma-buf/heaps/Kconfig

@@ -12,13 +12,3 @@ config DMABUF_HEAPS_CMA
 	  Choose this option to enable dma-buf CMA heap. This heap is backed
 	  by the Contiguous Memory Allocator (CMA). If your system has these
 	  regions, you should say Y here.
-
-config DMABUF_HEAPS_CMA_LEGACY
-	bool "Legacy DMA-BUF CMA Heap"
-	default y
-	depends on DMABUF_HEAPS_CMA
-	help
-	  Add a duplicate CMA-backed dma-buf heap with legacy naming derived
-	  from the CMA area's devicetree node, or "reserved" if the area is not
-	  defined in the devicetree. This uses the same underlying allocator as
-	  CONFIG_DMABUF_HEAPS_CMA.

drivers/dma-buf/heaps/cma_heap.c

@@ -22,6 +22,8 @@
 #include <linux/io.h>
 #include <linux/mm.h>
 #include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_reserved_mem.h>
 #include <linux/scatterlist.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
@@ -409,33 +411,30 @@ static int __init __add_cma_heap(struct cma *cma, const char *name)
 	return 0;
 }
 
-static int __init add_default_cma_heap(void)
+static int __init add_cma_heaps(void)
 {
 	struct cma *default_cma = dev_get_cma_area(NULL);
-	const char *legacy_cma_name;
+	unsigned int i;
 	int ret;
 
-	if (!default_cma)
-		return 0;
+	if (default_cma) {
+		ret = __add_cma_heap(default_cma, DEFAULT_CMA_NAME);
+		if (ret)
+			return ret;
+	}
 
-	ret = __add_cma_heap(default_cma, DEFAULT_CMA_NAME);
-	if (ret)
-		return ret;
+	for (i = 0; i < dma_areas_num; i++) {
+		struct cma *cma = dma_areas[i];
 
-	if (IS_ENABLED(CONFIG_DMABUF_HEAPS_CMA_LEGACY)) {
-		legacy_cma_name = cma_get_name(default_cma);
-		if (!strcmp(legacy_cma_name, DEFAULT_CMA_NAME)) {
-			pr_warn("legacy name and default name are the same, skipping legacy heap\n");
-			return 0;
+		ret = __add_cma_heap(cma, cma_get_name(cma));
+		if (ret) {
+			pr_warn("Failed to add CMA heap %s", cma_get_name(cma));
+			continue;
 		}
 
-		ret = __add_cma_heap(default_cma, legacy_cma_name);
-		if (ret)
-			pr_warn("failed to add legacy heap: %pe\n",
-				ERR_PTR(ret));
 	}
 
 	return 0;
 }
-module_init(add_default_cma_heap);
+module_init(add_cma_heaps);
 MODULE_DESCRIPTION("DMA-BUF CMA Heap");