[alsa-devel] [PATCH v2] Fix forward/rewind support in iec958 plugin

[Alexander E. Patrakov]

When forwarding or rewinding, the frame counter was not updated. This
could result in corrupted channel status words or misplaced Z-type
preamble.

Signed-off-by: Alexander E. Patrakov <patrakov at gmail.com>
---
v2: As suggested by David Henningsson, patch a copy of
snd_pcm_plugin_fast_ops at runtime instead of making all plugin finctions
non-static. But, contrary to his proposal, I made fast_ops just a part of
struct snd_pcm_iec958, because the needed lifetime is exactly the same.

I still have no hardware to test this, and I strongly suspect that the
patch is wrong, because nobody else uses dynamic allocation of fast_ops.
A potentially suspicious operation would be to place a plug on top of this,
because plug copies fast_ops around. However, each time it closes a slave,
it also resets fast_ops to something sane, or at least I think so.

 src/pcm/pcm_iec958.c | 37 ++++++++++++++++++++++++++++++++++++-
 src/pcm/pcm_plugin.c |  4 ++--
 src/pcm/pcm_plugin.h |  6 ++++++
 3 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/src/pcm/pcm_iec958.c b/src/pcm/pcm_iec958.c
index d81b0a1..0c61fc1 100644
--- a/src/pcm/pcm_iec958.c
+++ b/src/pcm/pcm_iec958.c
@@ -62,6 +62,7 @@ struct snd_pcm_iec958 {
 	unsigned char status[24];
 	unsigned int byteswap;
 	unsigned char preamble[3];	/* B/M/W or Z/X/Y */
+	snd_pcm_fast_ops_t fops;
 };
 
 enum { PREAMBLE_Z, PREAMBLE_X, PREAMBLE_Y };
@@ -416,6 +417,35 @@ static void snd_pcm_iec958_dump(snd_pcm_t *pcm, snd_output_t *out)
 	snd_pcm_dump(iec->plug.gen.slave, out);
 }
 
+static snd_pcm_sframes_t snd_pcm_iec958_rewind(snd_pcm_t *pcm, snd_pcm_uframes_t frames)
+{
+	unsigned int counter_decrement;
+	snd_pcm_iec958_t *iec = pcm->private_data;
+	snd_pcm_sframes_t result = snd_pcm_plugin_rewind(pcm, frames);
+	if (result <= 0)
+		return result;
+
+	counter_decrement = result % 192;
+	iec->counter += 192 - counter_decrement;
+	iec->counter %= 192;
+	return result;
+}
+
+static snd_pcm_sframes_t snd_pcm_iec958_forward(snd_pcm_t *pcm, snd_pcm_uframes_t frames)
+
+{
+	unsigned int counter_increment;
+	snd_pcm_iec958_t *iec = pcm->private_data;
+	snd_pcm_sframes_t result = snd_pcm_plugin_rewind(pcm, frames);
+	if (result <= 0)
+		return result;
+
+	counter_increment = result % 192;
+	iec->counter += counter_increment;
+	iec->counter %= 192;
+	return result;
+}
+
 static const snd_pcm_ops_t snd_pcm_iec958_ops = {
 	.close = snd_pcm_generic_close,
 	.info = snd_pcm_generic_info,
@@ -495,7 +525,12 @@ int snd_pcm_iec958_open(snd_pcm_t **pcmp, const char *name, snd_pcm_format_t sfo
 		return err;
 	}
 	pcm->ops = &snd_pcm_iec958_ops;
-	pcm->fast_ops = &snd_pcm_plugin_fast_ops;
+
+	iec->fops = snd_pcm_plugin_fast_ops;
+	iec->fops.rewind = snd_pcm_iec958_rewind;
+	iec->fops.forward = snd_pcm_iec958_forward;
+	pcm->fast_ops = &iec->fops;
+
 	pcm->private_data = iec;
 	pcm->poll_fd = slave->poll_fd;
 	pcm->poll_events = slave->poll_events;
diff --git a/src/pcm/pcm_plugin.c b/src/pcm/pcm_plugin.c
index 17157e8..4ddf10c 100644
--- a/src/pcm/pcm_plugin.c
+++ b/src/pcm/pcm_plugin.c
@@ -201,7 +201,7 @@ static snd_pcm_sframes_t snd_pcm_plugin_rewindable(snd_pcm_t *pcm)
 	return snd_pcm_mmap_hw_avail(pcm);
 }
 
-static snd_pcm_sframes_t snd_pcm_plugin_rewind(snd_pcm_t *pcm, snd_pcm_uframes_t frames)
+snd_pcm_sframes_t snd_pcm_plugin_rewind(snd_pcm_t *pcm, snd_pcm_uframes_t frames)
 {
 	snd_pcm_plugin_t *plugin = pcm->private_data;
 	snd_pcm_sframes_t n = snd_pcm_mmap_hw_avail(pcm);
@@ -229,7 +229,7 @@ static snd_pcm_sframes_t snd_pcm_plugin_forwardable(snd_pcm_t *pcm)
 	return snd_pcm_mmap_avail(pcm);
 }
 
-static snd_pcm_sframes_t snd_pcm_plugin_forward(snd_pcm_t *pcm, snd_pcm_uframes_t frames)
+snd_pcm_sframes_t snd_pcm_plugin_forward(snd_pcm_t *pcm, snd_pcm_uframes_t frames)
 {
 	snd_pcm_plugin_t *plugin = pcm->private_data;
 	snd_pcm_sframes_t n = snd_pcm_mmap_avail(pcm);
diff --git a/src/pcm/pcm_plugin.h b/src/pcm/pcm_plugin.h
index 7ee7c7f..19e82c3 100644
--- a/src/pcm/pcm_plugin.h
+++ b/src/pcm/pcm_plugin.h
@@ -58,8 +58,14 @@ typedef struct {
 	snd1_pcm_plugin_undo_read_generic
 #define snd_pcm_plugin_undo_write_generic \
 	snd1_pcm_plugin_undo_write_generic
+#define snd_pcm_plugin_rewind \
+	snd1_pcm_plugin_rewind
+#define snd_pcm_plugin_forward \
+	snd1_pcm_plugin_forward
 
 void snd_pcm_plugin_init(snd_pcm_plugin_t *plugin);
+snd_pcm_sframes_t snd_pcm_plugin_rewind(snd_pcm_t *pcm, snd_pcm_uframes_t frames);
+snd_pcm_sframes_t snd_pcm_plugin_forward(snd_pcm_t *pcm, snd_pcm_uframes_t frames);
 
 extern const snd_pcm_fast_ops_t snd_pcm_plugin_fast_ops;
 
-- 
1.9.2