[PATCH v3 4/4] ASoC: SOF: Intel: add .ack support for HDaudio platforms

[Pierre-Louis Bossart]

> I mean only about the use EXPLICIT_SYNC flag.  There has been already
> an info flag SYNC_APPLPTR, and this should suffice for your purpose.
> In a nutshell:
> 
> EXPLICIT_SYNC = disable both control and status mmaps
> SYNC_APPLPTR = disable only control mmap

Humm, are you sure Takashi? it's been a long time since we discussed
this and your initial direction was to disable both?

To quote your own words from
https://lore.kernel.org/alsa-devel/s5hfug51g0x.wl-tiwai@suse.de/

"In mmap mode, we transfer data on the mmap
buffer, and update appl_ptr via mmap control.  Both are done without
notification to the driver (which is intentional for avoiding the
context switching).

So we want to disable this optimization and always notify to the
driver.  Disabling mmap status/control is the straight hack as it
falls back to ioctl and then the driver can know the change."

I really don't mind changing, I don't have enough background on this,
just wanted to make sure that disabling the control mmap is sufficient
on paper before we re-run tests. Thanks!