Re: [alsa-devel] [PATCH] ALSA: hda: Use standard waitqueue for RIRB wakeup

[Takashi Iwai <tiwai@suse.de>]

On Fri, 13 Dec 2019 14:05:31 +0100,
Kai Vehmanen wrote:
> 
> Hey,
> 
> On Tue, 10 Dec 2019, Takashi Iwai wrote:
> 
> > This patch attempts to improve the situation by introducing the
> > standard waitqueue in the RIRB waiter side instead of polling.  The
> 
> this patch was part of the testing as well, so looks good. One minor
> nit only:
> 
> > @@ -216,6 +216,9 @@ void snd_hdac_bus_update_rirb(struct hdac_bus *bus)
> >  		else if (bus->rirb.cmds[addr]) {
> >  			bus->rirb.res[addr] = res;
> >  			bus->rirb.cmds[addr]--;
> > +			if (!bus->rirb.cmds[addr] &&
> > +			    waitqueue_active(&bus->rirb_wq))
> > +				wake_up(&bus->rirb_wq);
> 
> Checkpath would like to have a comment here:
> 
> WARNING: waitqueue_active without comment
> #77: FILE: sound/hda/hdac_controller.c:220:
> +                           waitqueue_active(&bus->rirb_wq))

Yeah, that was known to me, too.  Actually it's misleading; what
actually matters is the memory barrier or other synchronization there,
and this should work as is because of the current code path.
(Besides, majority of existing waitqueue_active() have no comments at
all :)

And, now I found wa_has_sleeper() as a better replacement of
waitqueue_active() that explicitly cares about synchronization.
So I'll change with this in a later patch (after unification to
hda-core).


thanks,

Takashi
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