[alsa-devel] ASoC: Failed to create DAPM debugfs

[Nicolin Chen]

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().

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:

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: