[v2] Fix forward/rewind support in iec958 plugin
diff mbox

Message ID 1398350406-10347-1-git-send-email-patrakov@gmail.com
State Accepted
Headers show

Commit Message

Alexander E. Patrakov April 24, 2014, 2:40 p.m. UTC
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@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(-)

Comments

Raymond Yau April 24, 2014, 11:02 p.m. UTC | #1
>
> When forwarding or rewinding, the frame counter was not updated. This
> could result in corrupted channel status words or misplaced Z-type
> preamble.

Do you mean it is the responsibility for a52 and dca plugin to return the
SAFE value returned by snd_pcm_rewindable and snd_pcm_forwardable since
they enocde the audio and padding zeros and write to IEC958 ?

>
> +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;
> +}
> +
Alexander E. Patrakov April 25, 2014, 6 a.m. UTC | #2
25.04.2014 05:02, Raymond Yau wrote:
>
>
> >
> > When forwarding or rewinding, the frame counter was not updated. This
> > could result in corrupted channel status words or misplaced Z-type
> > preamble.
>
> Do you mean it is the responsibility for a52 and dca plugin to return 
> the SAFE value returned by snd_pcm_rewindable and snd_pcm_forwardable 
> since they enocde the audio and padding zeros and write to IEC958 ?
>

Sorry, I don't understand the question, please reask differently if I am 
answering something else than what you mean here.

Neither a52 nor dca plugins use seeking under normal operation (when 
they themselves are not being seeked), they just write zeros when needed 
due to the IEC 61937-5 wrapping. Their implementations are in fact not 
seekable (they only pretend), and I will e-mail patches that enforce this.

What I mean in the patch is the following scenario involving an 
application that writes stereo data directly to the iec958 plugin.

1. Write 1920 samples.
2. Rewind 1919 samples.
3. Write 1919 samples.

Let's suppose that the counter was 0 initially, and the application 
pointer points at sample 0. Then, while encoding this to iec958 
subframes, the plugin would start the preamble sequence with Z. Result: 
ZYXYXYXYXY... in the output buffer after step 1. Z repeats every 192 
frames, as required by the standard. And the first subframe (with Z) now 
contains the first bit of the first status word. After writing 1920 
samples, the counter is still at 0, because it counts modulo 192.

After step 2, the application pointer points at sample 1, but the 
counter is 0 in the unpatched version and 1 in the patched one.

After step 3, the unpatched version writes the Z preamble and the first 
bit of the first status word. Result: ZYZYXYXYXY... The patched version 
writes the second bit of the first status word, i.e. just what should be 
in the buffer. Also, it puts the X preamble. Result: ZYXYXYXYXY..., just 
what there should be.

So, after the patch, the iec958 plugin properly supports arbitrary 
seeking, just like a normal hardware device, and should be just as 
usable by hypothetical seekable versions of the a52 and dca plugins.
Clemens Ladisch April 25, 2014, 8:09 a.m. UTC | #3
Raymond Yau wrote:
>> When forwarding or rewinding, the frame counter was not updated. This
>> could result in corrupted channel status words or misplaced Z-type
>> preamble.
>
> Do you mean it is the responsibility for a52 and dca plugin to return the
> SAFE value returned by snd_pcm_rewindable and snd_pcm_forwardable since
> they enocde the audio and padding zeros and write to IEC958 ?

The a52/dca plugins create data to be transferred over S/PDIF, but this
does not imply they use the iec958 plugin.

The iec958 plugin is used for sound cards that do not have a hardware
IEC958 encoder.  This is very unlikely nowadays.


Regards,
Clemens
Takashi Iwai April 28, 2014, 4:10 p.m. UTC | #4
At Thu, 24 Apr 2014 20:40:06 +0600,
Alexander E. Patrakov wrote:
> 
> 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@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.

The embedded fast_ops should work fine, so I applied the patch as is
now.  Let's see whether it really fixes the issues properly...


thanks,

Takashi

> 
>  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
> 
> _______________________________________________
> Alsa-devel mailing list
> Alsa-devel@alsa-project.org
> http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
>

Patch
diff mbox

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;