On Mon, Mar 30, 2026 at 10:59:48AM +0200, Marek Szyprowski wrote:

On 30.03.2026 10:40, Maxime Ripard wrote:

...

Commit 3a236f6a5cf2 ("dma: contiguous: Turn heap registration logic around") didn't remove one last call to dma_heap_cma_register_heap() that it removed, thus breaking the build.

That last call is in dma_contiguous_reserve(), to handle the registration of the default CMA region heap instance if it's declared in the device tree.

However, the default CMA region instance is already handled by retrieving it through dev_get_cma_area() in the CMA heap driver, so the call to dma_heap_cma_register_heap() wasn't actually needed.

Let's remove this call, the now unused function definition, its now empty header, and all includes of this header.

Fixes: 3a236f6a5cf2 ("dma: contiguous: Turn heap registration logic around") Reported-by: Mark Brown broonie@kernel.org Closes: https://lore.kernel.org/linux-next/acbjaDJ1a-YQC64d@sirena.co.uk/ Signed-off-by: Maxime Ripard mripard@kernel.org

---

drivers/dma-buf/heaps/cma_heap.c | 1 - include/linux/dma-buf/heaps/cma.h | 16 ---------------- kernel/dma/contiguous.c | 5 ----- 3 files changed, 22 deletions(-)

diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c index f8a3d87f3ccee9630383ba28502eb40b10671cc2..cc517ac68a0bec0788abcb338c03f530d169013b 100644 --- a/drivers/dma-buf/heaps/cma_heap.c +++ b/drivers/dma-buf/heaps/cma_heap.c @@ -12,11 +12,10 @@ #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> diff --git a/include/linux/dma-buf/heaps/cma.h b/include/linux/dma-buf/heaps/cma.h deleted file mode 100644 index e751479e21e703e24a5f799b4a7fc8bd0df3c1c4..0000000000000000000000000000000000000000 --- a/include/linux/dma-buf/heaps/cma.h +++ /dev/null @@ -1,16 +0,0 @@ -/* 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_ diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c index ad50512d71d3088a73e4b1ac02d6e6122374888e..9fe001c712339f8388d3f40cca3dfff3f707fcbf 100644 --- a/kernel/dma/contiguous.c +++ b/kernel/dma/contiguous.c @@ -40,11 +40,10 @@ #include <asm/page.h> #include <linux/memblock.h> #include <linux/err.h> #include <linux/sizes.h> -#include <linux/dma-buf/heaps/cma.h> #include <linux/dma-map-ops.h> #include <linux/cma.h> #include <linux/nospec.h> #ifdef CONFIG_CMA_SIZE_MBYTES @@ -270,14 +269,10 @@ void __init dma_contiguous_reserve(phys_addr_t limit) selected_limit, &dma_contiguous_default_area, fixed); if (ret) return;

• ret = dma_heap_cma_register_heap(dma_contiguous_default_area);
  

• if (ret)
  

• 	pr_warn("Couldn't register default CMA heap.");
  

After this change no dma-buf heap for the default CMA area is created if it has  not been specified in device-tree. This might be especially a problem for the non-dt systems.

I don't think that's the case? My understanding is that dma_contiguous_reserve() is called by the arch code, and will create that region only if it hasn't be set by the DT (that excerpt above is run only if !dma_contiguous_default_area).

However, for the DT case, dma_contiguous_default_area will be set by rmem_cma_setup() a bit below if linux,cma-default is set in the DT.

dma_contiguous_reserved() is called (on arm64 at least) through bootmem_init(), called as part of setup_arch().

rmem_cma_setup() is called through RESERVEDMEM_OF_DECLARE, so through __reserved_mem_init_node(), so, if we consider only the public functions, through:

* fdt_scan_reserved_mem_reg_nodes(), called by unflatten_device_tree(), called right before bootmem_init() in setup_arch();

* or fdt_scan_reserved_mem() and then early_init_fdt_scan_reserved_mem(), called in arm64_memblock_init(), itself called in setup_arch() earlier than both unflatten_device_tree(), and bootmem_init().

Thus, the DT case will run first and set dma_contiguous_default_area if relevant on that platform, and if it's not set, the non-DT case will set it up. Either way, dma_contiguous_default_area will be set.

The CMA heap runs much later using a regular module_init. It will retrieve dma_contiguous_default_area through dev_get_cma_area(), and will create a heap instance for the default area.

Am I misunderstanding something? Maxime