Re: [PATCH] dma/contiguous: Fix broken build

Maxime Ripard
2026-03-30T15:40:47Z

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On Mon, Mar 30, 2026 at 02:51:34PM +0200, Marek Szyprowski wrote:
> On 30.03.2026 13:41, Maxime Ripard wrote:
> > 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?
>
> The default CMA area is also optional for DT platforms.
>
> If DT doesn't provide such, it will be created based on the kernel
> cmdline cma= parameter or the default configuration defined in the
> kernel .config (this is also true for the non-dt platforms). I know
> that for most Android GKI systems the default CMA area will be defined
> in DT, but I see no reason to disable dma-buf heap support for the
> default CMA area if it has been instantiated from kernel cmdline or
> .config.

I think I see what you mean now, thanks! Sending a v2.

Maxime

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