dma-buf: heaps: Give default CMA heap a fixed name

The CMA heap's name in devtmpfs can vary depending on how the heap is
defined. Its name defaults to "reserved", but if a CMA area is defined
in the devicetree, the heap takes on the devicetree node's name, such as
"default-pool" or "linux,cma". To simplify naming, unconditionally name
it "default_cma_region", but keep a legacy node in place backed by the
same underlying allocator for backwards compatibility.

Reviewed-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Jared Kangas <jkangas@redhat.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://lore.kernel.org/r/20250610131231.1724627-4-jkangas@redhat.com

Author: rh-jkangas

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

@@ -21,5 +21,8 @@ following heaps:
    usually created either through the kernel commandline through the
    ``cma`` parameter, a memory region Device-Tree node with the
    ``linux,cma-default`` property set, or through the ``CMA_SIZE_MBYTES`` or
-   ``CMA_SIZE_PERCENTAGE`` Kconfig options. Depending on the platform, it
-   might be called ``reserved``, ``linux,cma``, or ``default-pool``.
+   ``CMA_SIZE_PERCENTAGE`` Kconfig options. The heap's name in devtmpfs is
+   ``default_cma_region``. For backwards compatibility, when the
+   ``DMABUF_HEAPS_CMA_LEGACY`` Kconfig option is set, a duplicate node is
+   created following legacy naming conventions; the legacy name might be
+   ``reserved``, ``linux,cma``, or ``default-pool``.

drivers/dma-buf/heaps/Kconfig

@@ -12,3 +12,13 @@ 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

@@ -9,6 +9,9 @@
  * Copyright (C) 2019 Texas Instruments Incorporated - http://www.ti.com/
  *	Andrew F. Davis <afd@ti.com>
  */
+
+#define pr_fmt(fmt) "cma_heap: " fmt
+
 #include <linux/cma.h>
 #include <linux/dma-buf.h>
 #include <linux/dma-heap.h>
@@ -22,6 +25,7 @@
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 
+#define DEFAULT_CMA_NAME "default_cma_region"
 
 struct cma_heap {
 	struct dma_heap *heap;
@@ -394,15 +398,29 @@ static int __init __add_cma_heap(struct cma *cma, const char *name)
 static int __init add_default_cma_heap(void)
 {
 	struct cma *default_cma = dev_get_cma_area(NULL);
+	const char *legacy_cma_name;
 	int ret;
 
 	if (!default_cma)
 		return 0;
 
-	ret = __add_cma_heap(default_cma, cma_get_name(default_cma));
+	ret = __add_cma_heap(default_cma, DEFAULT_CMA_NAME);
 	if (ret)
 		return ret;
 
+	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(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);