DMA memory is currently allocated for the soundcard device, which is a
virtual device added for the sole purpose of "stitching" together the
audio device. It is not a real device and therefore doesn't have a DMA
mask or a description of the path to and from memory of accesses.

Memory accesses really originate from the ADMA controller that provides
the DMA channels used by the PCM component. However, since the DMA
memory is allocated up-front and the DMA channels aren't known at that
point, there is no way of knowing the DMA channel provider at allocation
time.

The next best physical device in the memory path is the ADMAIF. Use it
as the device to allocate DMA memory to. iommus and interconnects device
tree properties can thus be added to the ADMAIF device tree node to
describe the memory access path for audio.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20210708103432.1690385-2-thierry.reding@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>