[alsa-devel] [PATCH] ASoC: rsnd: stop all working stream when .remove

[Takashi Iwai]

On Tue, 05 Sep 2017 09:40:11 +0200,
Kuninori Morimoto wrote:
> 
> Hi Takashi-san
> 
> Thank you for your feedback
> 
> > This isn't something you shouldn't fiddle with the codec layer.
> > If the driver gets removed during the operation, you have to cancel 
> > the operation and sync with it in a proper way, then proceed the rest 
> > of the remove, not only a codec-specific resource management.
> (snip)
> > Here I mentioned the codec driver, but it's applied to each lower-level
> > component.  It'd need some graceful way to communicate with the
> > top-level card to assure the removal of the component.
> 
> I agree.
> I can't access to source code now (I'm in business-trip), but my head-acke is that kernel doesn't check return value from .remove when unbind case.
> Thus, we can't "cancel" remove operation.
> I'm happy if you can confirm it.

Right, you can't cancel or return an error at that point.  That is,
you'd need to sync (wait) until the all top-level operations are
canceled at remove callback.

For example, snd_card_free() processes the disconnection procedure at
first, then waits for the completion.  That's how the hot-unplug works
safely.  It's implemented, at least, in the top-level driver removal.

Now for the lower level driver, you'd need a similar strategy; notify
to the toplevel for hot-unplug (disconnect in ALSA), and sync with the
stop operation, then continue the rest of its own remove procedure.


thanks,

Takashi