[PATCH] ALSA: hda - Don't register a cb func if it is registered already

[Takashi Iwai]

On Wed, 30 Sep 2020 11:28:59 +0200,
Jaroslav Kysela wrote:
> 
> Dne 30. 09. 20 v 11:21 Takashi Iwai napsal(a):
> > On Wed, 30 Sep 2020 09:19:50 +0200,
> > Jaroslav Kysela wrote:
> >>
> >> Dne 30. 09. 20 v 7:51 Hui Wang napsal(a):
> >>> If the caller of enable_callback_mst() passes a cb func, the callee
> >>> function will malloc memory and link this cb func to the list
> >>> unconditionally. This will introduce problem if caller is in the
> >>> hda_codec_ops.init() since the init() will be repeatedly called in the
> >>> codec rt_resume().
> >>>
> >>> So far, the patch_hdmi.c and patch_ca0132.c call enable_callback_mst()
> >>> in the hda_codec_ops.init().
> >>
> >> Won't be better to handle this double invocation at the callback call time? I
> >> believe that some refcounting and pointing to one allocated callback structure
> >> for all instances is better.
> > 
> > IMO, Hui's fix is correct in this case; otherwise it'll result in
> > endless number of allocations at each time the runtime resume is
> > performed.  So I'm going to take it as is.
> 
> I meant to allocate the structure only once with refcounting and multiple
> invocation protection. In the proposed change, you lose the
> bindings.

AFAIUC, it won't lose any functionality.
snd_hda_jack_detect_enable_callback() would chain the callback
function if a jack object has been already created, and this
additional check will just prevent the doubly registration of the very
same callback when called multiple times.


thanks,

Takashi