+ /* set runtime config */
+ runtime->hw.info = SNDRV_PCM_INFO_MMAP |
+ SNDRV_PCM_INFO_MMAP_VALID |
+ SNDRV_PCM_INFO_INTERLEAVED |
+ SNDRV_PCM_INFO_PAUSE |
+ SNDRV_PCM_INFO_RESUME |
+ SNDRV_PCM_INFO_NO_PERIOD_WAKEUP;
Does SOF support the full resume? That is, the stream gets resumed
at
the exact position that was suspended. Most devices can't, hence
they
don't set *_INFO_RESUME flag and let user-space restarting.
Hi Takashi,
Thanks for your comment. The SOF driver definitely cannot guarantee to
resume from the exact same position due to the fact that triggers for
the host dma and link dma are not synchronized and also IPC scheduling
will affect this. So we should remove INOF_RESUME from hw.info.
I do one follow up question for you. When a stream resumes/restarts
after suspend, we have the need for restoring the hw_params in the SOF
driver prior to handling the START trigger. I noticed that the
legacy/skylake driver does not seem to do this though. Do you have any
insights on what we might be missing in the SOF driver?
So, SOF mandates the re-setup of the hw params in BE at resume?
Then the right place to do is in the prepare callback. Without
SNDRV_PCM_INFO_RESUME flag, the PCM core won't trigger RESUME, but
returns -ENOSYS. Then user-space will do prepare, and start with the
normal trigger.
Takashi, some of us at Intel are a bit nervous about returning an
error to force the application to jump to its error-handling code
(typically only done for xruns and not always rock-solid) and as a
side effect get a prepare ioctl. I checked that e.g. CRAS does support
this mode but I wonder how many application developers know about
this. I personally didn't.
Essentially all applications are supposed to do so. There are only
few drivers that support really the full resume. Some drivers set the
flag, but many of them must be incorrect, especially ASoC ones.
Moreover, it seems that the default behavior is rather to support
RESUME, even if the hardware can't precisely restart from the same
position, so we are concerned about exposing new errors when SOF is
selected instead of legacy drivers (Baytrail, Atom-SST and
Skylake-SST).
In short, is this really your recommendation to remove this
INFO_RESUME flag? And if yes, should we demote all existing Intel
drivers and remove this flag as well?
Yes, better to start with less -- especially if this allows us to
simplify the code a lot.
ok, thanks for confirming. we'll remove the INFO_RESUME flag in SOF and
follow-up with the removal on all other Intel drivers. Thanks for
enlightening us on this.
-Pierre
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