ALSA: qc_audio_offload: try to reduce address space confusion

ALSA: qc_audio_offload: try to reduce address space confusion

uaudio_transfer_buffer_setup() allocates a buffer for the subs->dev
device, and the returned address for the buffer is a CPU local virtual
address that may or may not be in the linear mapping, as well as a DMA
address token that is accessible by the USB device, and this in turn
may or may not correspond to the physical address.

The use in the driver however assumes that these addresses are the
linear map and the CPU physical address, respectively. Both are
nonportable here, but in the end only the virtual address gets
used by converting it to a physical address that gets mapped into
a second iommu.

Make this more explicit by pulling the conversion out first
and warning if it is not part of the linear map, and using the
actual physical address to map into the iommu in place of the
dma address that may already be iommu-mapped into the usb host.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20250513123442.159936-4-arnd@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>