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(-)
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.");
}
}
void __weak
dma_contiguous_early_fixup(phys_addr_t base, unsigned long size)
---
base-commit: f3948c8ed5ea206e87ea2375aebdbabc2064356a
change-id: 20260330-dma-build-fix-706a4feb0e0f
Best regards,
--
Maxime Ripard <mripard@kernel.org>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.
> }
> }
>
> void __weak
> dma_contiguous_early_fixup(phys_addr_t base, unsigned long size)
>
>
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
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
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.
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
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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