Re: [PATCH v2 0/3] iio: buffer: Fix DMABUF mapping in some systems

[David Lechner <dlechner@baylibre.com>]

On 10/6/25 11:06 AM, Nuno Sá via B4 Relay wrote:
> This series fixes an issue with DMABUF support in the IIO subsystem where
> the wrong DMA device could be used for buffer mapping operations. This
> becomes critical on systems like Xilinx/AMD ZynqMP Ultrascale where memory
> can be mapped above the 32-bit address range.
> 
> Problem:
> --------
> The current IIO DMABUF implementation assumes it can use the parent device
> of the IIO device for DMA operations. However, this device may not have
> the appropriate DMA mask configuration for accessing high memory addresses.
> On systems where memory is mapped above 32-bits, this leads to the use of
> bounce buffers through swiotlb, significantly impacting performance.
> 
> Solution:
> ---------
> This series introduces a new .get_dma_dev() callback in the buffer access
> functions that allows buffer implementations to specify the correct DMA
> device that should be used for DMABUF operations. The DMA buffer
> infrastructure implements this callback to return the device that actually
> owns the DMA channel, ensuring proper memory mapping without bounce buffers.
> 
> Changes:
> --------
> 1. Add .get_dma_dev() callback to iio_buffer_access_funcs and update core
>    DMABUF code to use it when available
> 2. Implement the callback in the DMA buffer infrastructure
> 3. Wire up the callback in the dmaengine buffer implementation
> 
> This ensures that DMABUF operations use the device with the correct DMA
> configuration, eliminating unnecessary bounce buffer usage and improving
> performance on high-memory systems.
> 
> (AI generated cover. I would not be this formal but I guess is not
> that bad :))
> 
> ---
> Changes in v2:
> - Dropped Fixes tags on the first two patches and Cc stable them instead
>   (as prerequisites for the third patch). 
> - Link to v1: https://lore.kernel.org/r/20251002-fix-iio-dmabuf-get-dma-device-v1-0-c1c9945029d0@analog.com

Did you not care for my other suggestions in v1?