linux-kernel - [PATCH v2 2/2] dma-buf: heaps: Give default CMA heap a fixed name

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Message-ID: <20250422191939.555963-3-jkangas@redhat.com>
Date: Tue, 22 Apr 2025 12:19:39 -0700
From: Jared Kangas <jkangas@...hat.com>
To: sumit.semwal@...aro.org,
	benjamin.gaignard@...labora.com,
	Brian.Starkey@....com,
	jstultz@...gle.com,
	tjmercier@...gle.com,
	christian.koenig@....com
Cc: mripard@...nel.org,
	linux-media@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	linaro-mm-sig@...ts.linaro.org,
	linux-kernel@...r.kernel.org,
	Jared Kangas <jkangas@...hat.com>
Subject: [PATCH v2 2/2] 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, just name it
"default_cma", and keep a legacy node in place backed by the same
underlying structure for backwards compatibility.

Signed-off-by: Jared Kangas <jkangas@...hat.com>
---
 Documentation/userspace-api/dma-buf-heaps.rst | 11 +++++++----
 drivers/dma-buf/heaps/Kconfig                 | 10 ++++++++++
 drivers/dma-buf/heaps/cma_heap.c              | 14 +++++++++++++-
 3 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/Documentation/userspace-api/dma-buf-heaps.rst b/Documentation/userspace-api/dma-buf-heaps.rst
index 535f49047ce64..577de813ba461 100644
--- a/Documentation/userspace-api/dma-buf-heaps.rst
+++ b/Documentation/userspace-api/dma-buf-heaps.rst
@@ -19,7 +19,10 @@ following heaps:
  - The ``cma`` heap allocates physically contiguous, cacheable,
    buffers. Only present if a CMA region is present. Such a region is
    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`` 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. The heap's name in devtmpfs is
+   ``default_cma``. 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``.
diff --git a/drivers/dma-buf/heaps/Kconfig b/drivers/dma-buf/heaps/Kconfig
index a5eef06c42264..83f3770fa820a 100644
--- a/drivers/dma-buf/heaps/Kconfig
+++ b/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 "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.
diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c
index e998d8ccd1dc6..cd742c961190d 100644
--- a/drivers/dma-buf/heaps/cma_heap.c
+++ b/drivers/dma-buf/heaps/cma_heap.c
@@ -22,6 +22,7 @@
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 
+#define DEFAULT_CMA_NAME "default_cma"
 
 struct cma_heap {
 	struct dma_heap *heap;
@@ -394,15 +395,26 @@ 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;
 
+	legacy_cma_name = cma_get_name(default_cma);
+
+	if (IS_ENABLED(CONFIG_DMABUF_HEAPS_CMA_LEGACY) &&
+	    strcmp(legacy_cma_name, DEFAULT_CMA_NAME)) {
+		ret = __add_cma_heap(default_cma, legacy_cma_name);
+		if (ret)
+			pr_warn("cma_heap: failed to add legacy heap: %pe\n",
+				ERR_PTR(-ret));
+	}
+
 	return 0;
 }
 module_init(add_default_cma_heap);
-- 
2.49.0