linux-kernel - [PATCH v7 2/5] dma-buf: heaps: cma: Register list of CMA regions at boot

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Message-Id: <20250721-dma-buf-ecc-heap-v7-2-031836e1a942@kernel.org>
Date: Mon, 21 Jul 2025 13:17:31 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Rob Herring <robh@...nel.org>, Saravana Kannan <saravanak@...gle.com>, 
 Sumit Semwal <sumit.semwal@...aro.org>, 
 Benjamin Gaignard <benjamin.gaignard@...labora.com>, 
 Brian Starkey <Brian.Starkey@....com>, John Stultz <jstultz@...gle.com>, 
 "T.J. Mercier" <tjmercier@...gle.com>, 
 Christian König <christian.koenig@....com>, 
 Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, 
 Marek Szyprowski <m.szyprowski@...sung.com>, 
 Robin Murphy <robin.murphy@....com>, Jonathan Corbet <corbet@....net>
Cc: Andrew Davis <afd@...com>, Jared Kangas <jkangas@...hat.com>, 
 Mattijs Korpershoek <mkorpershoek@...nel.org>, devicetree@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-media@...r.kernel.org, 
 dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org, 
 iommu@...ts.linux.dev, linux-doc@...r.kernel.org, 
 Maxime Ripard <mripard@...nel.org>
Subject: [PATCH v7 2/5] dma-buf: heaps: cma: Register list of CMA regions
 at boot

In order to create a CMA heap instance for each CMA region found in the
system, we need to register each of these instances.

While it would appear trivial, the CMA regions are created super early
in the kernel boot process, before most of the subsystems are
initialized. Thus, we can't just create an exported function to create a
heap from the CMA region being initialized.

What we can do however is create a two-step process, where we collect
all the CMA regions into an array early on, and then when we initialize
the heaps we iterate over that array and create the heaps from the CMA
regions we collected.

Signed-off-by: Maxime Ripard <mripard@...nel.org>
---
 MAINTAINERS                       |  1 +
 drivers/dma-buf/heaps/cma_heap.c  | 14 ++++++++++++++
 include/linux/dma-buf/heaps/cma.h | 16 ++++++++++++++++
 3 files changed, 31 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index fad6cb025a1918beec113b576cf28b76151745ef..deb6930f28c82a7257f1d4610b9bc010de62a0c9 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7095,10 +7095,11 @@ T:	git https://gitlab.freedesktop.org/drm/misc/kernel.git
 F:	Documentation/driver-api/dma-buf.rst
 F:	Documentation/userspace-api/dma-buf-alloc-exchange.rst
 F:	drivers/dma-buf/
 F:	include/linux/*fence.h
 F:	include/linux/dma-buf.h
+F:	include/linux/dma-buf/
 F:	include/linux/dma-resv.h
 K:	\bdma_(?:buf|fence|resv)\b

 DMA GENERIC OFFLOAD ENGINE SUBSYSTEM
 M:	Vinod Koul <vkoul@...nel.org>
diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c
index 0df007111975447d555714d61ead9699287fd65a..2a901af635ed76cdb085915c03258c235e302792 100644
--- a/drivers/dma-buf/heaps/cma_heap.c
+++ b/drivers/dma-buf/heaps/cma_heap.c
@@ -12,10 +12,11 @@

 #define pr_fmt(fmt) "cma_heap: " fmt

 #include <linux/cma.h>
 #include <linux/dma-buf.h>
+#include <linux/dma-buf/heaps/cma.h>
 #include <linux/dma-heap.h>
 #include <linux/dma-map-ops.h>
 #include <linux/err.h>
 #include <linux/highmem.h>
 #include <linux/io.h>
@@ -25,10 +26,23 @@
 #include <linux/slab.h>
 #include <linux/vmalloc.h>

 #define DEFAULT_CMA_NAME "default_cma_region"

+static struct cma *dma_areas[MAX_CMA_AREAS] __initdata;
+static unsigned int dma_areas_num __initdata;
+
+int __init dma_heap_cma_register_heap(struct cma *cma)
+{
+	if (dma_areas_num >= ARRAY_SIZE(dma_areas))
+		return -EINVAL;
+
+	dma_areas[dma_areas_num++] = cma;
+
+	return 0;
+}
+
 struct cma_heap {
 	struct dma_heap *heap;
 	struct cma *cma;
 };

diff --git a/include/linux/dma-buf/heaps/cma.h b/include/linux/dma-buf/heaps/cma.h
new file mode 100644
index 0000000000000000000000000000000000000000..e751479e21e703e24a5f799b4a7fc8bd0df3c1c4
--- /dev/null
+++ b/include/linux/dma-buf/heaps/cma.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef DMA_BUF_HEAP_CMA_H_
+#define DMA_BUF_HEAP_CMA_H_
+
+struct cma;
+
+#ifdef CONFIG_DMABUF_HEAPS_CMA
+int dma_heap_cma_register_heap(struct cma *cma);
+#else
+static inline int dma_heap_cma_register_heap(struct cma *cma)
+{
+	return 0;
+}
+#endif // CONFIG_DMABUF_HEAPS_CMA
+
+#endif // DMA_BUF_HEAP_CMA_H_

-- 
2.50.1