On Mon, Aug 05, 2019 at 11:22:03AM +0200, Takashi Iwai wrote:

This won't work as expected, unfortunately.  It's a bit tricky check,
since the driver may have its own mmap implementation via
substream->ops->mmap, and the dma_buffer.dev.dev might point to
another object depending on the dma_buffer.dev.type.

So please replace with something like below:

From my gut feeling I'd reorder it a bit to make it more clear like
this:

http://git.infradead.org/users/hch/misc.git/commitdiff/958fccf54d00c16740522f818d23f9350498e911

if this is fine it'll be in the next version, waiting for a little more
feedback on the other patches.