When the CAL driver stops streaming, it will shut everything down
without waiting for the current frame to finish. This leaves the CAL DMA
in a slightly undefined state, and when CAL DMA is enabled when the
stream is started the next time, the old DMA transfer will continue.

It is not clear if the old DMA transfer continues with the exact
settings of the original transfer, or is it a mix of old and new
settings, but in any case the end result is memory corruption as the
destination memory address is no longer valid.

I could not find any way to ensure that any old DMA transfer would be
discarded, except perhaps full CAL reset. But we cannot do a full reset
when one port is getting enabled, as that would reset both ports.

This patch tries to make sure that the DMA transfer is finished properly
when the stream is being stopped. I say "tries", as, as mentioned above,
I don't see a way to force the DMA transfer to finish. I believe this
fixes the corruptions for normal cases, but if for some reason the DMA
of the final frame would stall a lot, resulting in timeout in the code
waiting for the DMA to finish, we'll again end up with unfinished DMA
transfer. However, I don't know what could cause such a timeout.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>