[PATCH 09/10] ALSA: pcm: Add snd_pcm_ops for snd_pcm_link()

twischer
2019-03-26T07:51:12Z

From: Timo Wischer <twischer@de.adit-jv.com>

snd_pcm_link() can be called by the user as long as the device is not
yet started. Therefore currently a driver which wants to iterate over
the linked substreams has to do this at the start trigger. But the start
trigger should not block for a long time. Therefore there is no callback
which can be used to iterate over the linked substreams without delaying
the start trigger.
This patch introduces a new callback function which will be called after
the linked substream list was updated by snd_pcm_link(). This callback
function is allowed to block for a longer time without interfering the
synchronized start up of linked substreams.

Signed-off-by: Timo Wischer <twischer@de.adit-jv.com>
---
include/sound/pcm.h | 1 +
sound/core/pcm_native.c | 29 +++++++++++++++++++++++++++++
2 files changed, 30 insertions(+)

diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index 18bd8c3..a7e5dd2 100644
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -90,6 +90,7 @@ struct snd_pcm_ops {
unsigned long offset);
int (*mmap)(struct snd_pcm_substream *substream, struct vm_area_struct *vma);
int (*ack)(struct snd_pcm_substream *substream);
+ int (*link_changed)(struct snd_pcm_substream *substream);
};

/*
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index f731f90..57a8a66 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -1981,6 +1981,27 @@ static bool is_pcm_file(struct file *file)
/*
* PCM link handling
*/
+/* Note: call with snd_pcm_link_rwsem locked */
+static int snd_pcm_link_changed(struct snd_pcm_substream * const substream)
+{
+ struct snd_pcm_substream *s;
+
+ /* snd_pcm_link_rwsem is down whenever the link_list is changed.
+ * Therefore this lock is sufficent for the iteration.
+ */
+ snd_pcm_group_for_each_entry(s, substream) {
+ int err;
+
+ if (!s->ops->link_changed)
+ continue;
+ err = s->ops->link_changed(s);
+ if (err < 0)
+ return err;
+ }
+
+ return 0;
+}
+
static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
{
int res = 0;
@@ -2030,6 +2051,9 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
snd_pcm_group_assign(substream1, target_group);
snd_pcm_stream_unlock(substream1);
snd_pcm_group_unlock_irq(target_group, nonatomic);
+
+ if (res >= 0)
+ res = snd_pcm_link_changed(substream);
_end:
up_write(&snd_pcm_link_rwsem);
_nolock:
@@ -2076,6 +2100,11 @@ static int snd_pcm_unlink(struct snd_pcm_substream *substream)
snd_pcm_group_unlock_irq(group, nonatomic);
if (do_free)
kfree(group);
+ if (res >= 0)
+ res = snd_pcm_link_changed(substream);
+ /* Also signal substream which was removed */
+ if (res >= 0 && substream->ops->link_changed)
+ res = substream->ops->link_changed(substream);

_end:
up_write(&snd_pcm_link_rwsem);
--
2.7.4