rmem_dma_device_init() drops the return value of
dma_assign_coherent_memory() and always reports success. That call fails
with -EBUSY when the device already has a coherent pool, and the file
allows only "*one* such region of memory" per device.

of_reserved_mem_device_init_by_idx() reads the zero as success. It logs
"assigned reserved memory node" for a region that was not assigned and
records the pairing, so of_reserved_mem_device_release() later runs
rmem_dma_device_release() for it. That clears dev->dma_mem without
looking at which region it was called for, dropping the pool the device
did get and leaving it on ordinary memory.

dma_declare_coherent_memory() checks the same call and releases the
memory on failure, and rmem_swiotlb_device_init() propagates its own
errors. Return the error here as well, so a device tree that assigns two
pools to one device fails the probe instead of half working.

Fixes: 7bfa5ab6fa1b ("drivers: dma-coherent: add initialization from device tree")
Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@gmail.com>
---
Compile-tested only, with CONFIG_DMA_DECLARE_COHERENT=y and
CONFIG_OF_RESERVED_MEM=y. I do not have a board that assigns two
shared-dma-pool regions to one device; the release path was traced
through of_reserved_mem_device_release() and rmem_dma_device_release()
rather than observed.

 kernel/dma/coherent.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/dma/coherent.c b/kernel/dma/coherent.c
index 45bbae947f4b..4d0266893bcc 100644
--- a/kernel/dma/coherent.c
+++ b/kernel/dma/coherent.c
@@ -352,8 +352,7 @@ static int rmem_dma_device_init(struct reserved_mem *rmem, struct device *dev)
 	    min_not_zero(dev->coherent_dma_mask, dev->bus_dma_limit))
 		dev_warn(dev, "reserved memory is beyond device's set DMA address range\n");
 
-	dma_assign_coherent_memory(dev, mem);
-	return 0;
+	return dma_assign_coherent_memory(dev, mem);
 }
 
 static void rmem_dma_device_release(struct reserved_mem *rmem,
-- 
2.53.0

On 05.09.2026 09:47, Donggeun Yoo wrote:
> rmem_dma_device_init() drops the return value of
> dma_assign_coherent_memory() and always reports success. That call fails
> with -EBUSY when the device already has a coherent pool, and the file
> allows only "*one* such region of memory" per device.
>
> of_reserved_mem_device_init_by_idx() reads the zero as success. It logs
> "assigned reserved memory node" for a region that was not assigned and
> records the pairing, so of_reserved_mem_device_release() later runs
> rmem_dma_device_release() for it. That clears dev->dma_mem without
> looking at which region it was called for, dropping the pool the device
> did get and leaving it on ordinary memory.
>
> dma_declare_coherent_memory() checks the same call and releases the
> memory on failure, and rmem_swiotlb_device_init() propagates its own
> errors. Return the error here as well, so a device tree that assigns two
> pools to one device fails the probe instead of half working.
>
> Fixes: 7bfa5ab6fa1b ("drivers: dma-coherent: add initialization from device tree")
> Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@gmail.com>

Applied to dma-mapping-fixes, thanks!

> ---
> Compile-tested only, with CONFIG_DMA_DECLARE_COHERENT=y and
> CONFIG_OF_RESERVED_MEM=y. I do not have a board that assigns two
> shared-dma-pool regions to one device; the release path was traced
> through of_reserved_mem_device_release() and rmem_dma_device_release()
> rather than observed.
>
>  kernel/dma/coherent.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/kernel/dma/coherent.c b/kernel/dma/coherent.c
> index 45bbae947f4b..4d0266893bcc 100644
> --- a/kernel/dma/coherent.c
> +++ b/kernel/dma/coherent.c
> @@ -352,8 +352,7 @@ static int rmem_dma_device_init(struct reserved_mem *rmem, struct device *dev)
>  	    min_not_zero(dev->coherent_dma_mask, dev->bus_dma_limit))
>  		dev_warn(dev, "reserved memory is beyond device's set DMA address range\n");
>  
> -	dma_assign_coherent_memory(dev, mem);
> -	return 0;
> +	return dma_assign_coherent_memory(dev, mem);
>  }
>  
>  static void rmem_dma_device_release(struct reserved_mem *rmem,

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland