Re: ASoC: Failed to create DAPM debugfs

[Lars-Peter Clausen <lars@metafoo.de>]

On 04/09/2015 10:45 AM, Nicolin Chen wrote:
> On Thu, Apr 09, 2015 at 10:29:39AM +0200, Lars-Peter Clausen wrote:
>> On 04/09/2015 10:22 AM, Nicolin Chen wrote:
>>> On Thu, Apr 09, 2015 at 09:39:09AM +0200, Lars-Peter Clausen wrote:
>>>
>>>> The whole thing is a bit confusing. The message you get is what
>>>> you'd get if the 'dapm' sub-directory in the card debugfs directory
>>>> can not be created. One of the few reasons why it would fail is if
>>>> it already existed, but we should never register two dapm contexts
>>>> for the card, so that's a bit strange. One of the few reasons I can
>>>> imagine this could happen is if the parent directory could not be
>>>> created and now we try to create multiple dapm directories at the
>>>> top-level.
>>>>
>>>> Try to do some more debugging and see why and where exactly things
>>>> go wrong. Can you also try this:
>>>>
>>>> diff --git a/sound/soc/soc-dapm.c b/sound/soc/soc-dapm.c
>>>> index b6f8820..7810262 100644
>>>> --- a/sound/soc/soc-dapm.c
>>>> +++ b/sound/soc/soc-dapm.c
>>>> @@ -1898,6 +1898,11 @@
>>>>   {
>>>>   	struct dentry *d;
>>>>
>>>> +	if (!parent) {
>>>> +		dev_warn(dapm->dev, "No debugfs parent!\n");
>>>
>>> I tried, yes, the parent is NULL. And I did a little tracing and found
>>> that the card->debugfs_root, which is NULL, should be initialized in
>>> the soc_init_card_debugfs() while snd_soc_dapm_debugfs_init() seems
>>> to access this card->debugfs_root before calling soc_init_card_debugfs().
>>>
>>> I think I must have missed something over here....
>>
>> Looks like this is the culprit: http://git.kernel.org/cgit/linux/kernel/git/broonie/sound.git/commit/?h=for-next&id=4e2576bd36a12e78ac3786d05b99a820dffe687f
>>
>
> I think this patch didn't move the snd_init_card_debugfs() backwards.
> It just wrapped the call at the end of snd_soc_instantiate_card().

Previously it was called before snd_soc_instantiate_card() and there is a 
lot of things inside snd_soc_instantiate_card() that expect the card debugfs 
directory to exist. So those now all end up at the top-level.

>
> But the snd_soc_dapm_debugfs_init() call that's going to access the
> card->debugfs_root was put before the snd_init_card_debugfs() at the
> first place....
>
> I'm not sure if this could be a fix but the warning is actually gone:

There is more stuff that expects the directory to exist in 
snd_soc_instantiate_card() so we need to move soc_init_card_debugfs() 
further up. See the patch I just sent.

>
> diff --git a/sound/soc/soc-core.c b/sound/soc/soc-core.c
> index 2801578..0412795 100644
> --- a/sound/soc/soc-core.c
> +++ b/sound/soc/soc-core.c
> @@ -1560,10 +1560,6 @@ static int snd_soc_instantiate_card(struct snd_soc_card *card)
>   	card->dapm.card = card;
>   	list_add(&card->dapm.list, &card->dapm_list);
>
> -#ifdef CONFIG_DEBUG_FS
> -	snd_soc_dapm_debugfs_init(&card->dapm, card->debugfs_card_root);
> -#endif
> -
>   #ifdef CONFIG_PM_SLEEP
>   	/* deferred resume work */
>   	INIT_WORK(&card->deferred_resume_work, soc_resume_deferred);
> @@ -1686,6 +1682,10 @@ static int snd_soc_instantiate_card(struct snd_soc_card *card)
>
>   	soc_init_card_debugfs(card);
>
> +#ifdef CONFIG_DEBUG_FS
> +	snd_soc_dapm_debugfs_init(&card->dapm, card->debugfs_card_root);
> +#endif
> +
>   	return 0;
>
>   probe_aux_dev_err:
>