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

[Jaroslav Kysela]

Dne 30. 09. 20 v 11:39 Takashi Iwai napsal(a):
> 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.

Ok, I see, the lookup is codec / nid / dev_id so in this case the multiple
callback assignments are really not desired. Thanks for the explanation.

					Jaroslav

-- 
Jaroslav Kysela <perex at perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.