ALSA: firewire-lib/dice/speakers: Add common PCM constraints for AMDTP streams

This commit adds common PCM constraints according to current firewire-lib
implementation.

1.Maximum width for each sample is limited by 24.
AM824 in IEC 61883-6 can deliver 24bit data.

2. Minimum time for period is 5msec.
Apply the old value. For shorter latency, further works are needed.

3. In blocking mode, frames per period/buffer is aligned to 32.
Each packet can include some frames depending on its sampling rate. In
blocking mode, the number equals to SYT_INTERVAL. Currently firewire-lib
can schedule snd_pcm_period_elapsed() for each packet. So, for accurate
PCM interrupt, the number of frames per period/buffer should be aligned
to SYT_INTERVAL.
Currently firewire-lib is lack of better rules to achieve this. So LCM of
each value of SYT_INTERVALs (=32) is applied. This can be improved for
further work.

[Fixed the compile error due to the missing "&" by tiwai]

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

4 files changed, 61 insertions, 23 deletions

diff --git a/sound/firewire/amdtp.c b/sound/firewire/amdtp.c
index 3475b76b3304..ac8c35830cd9 100644
--- a/sound/firewire/amdtp.c
+++ b/sound/firewire/amdtp.c
@@ -13,6 +13,7 @@
 #include <linux/slab.h>
 #include <linux/sched.h>
 #include <sound/pcm.h>
+#include <sound/pcm_params.h>
 #include <sound/rawmidi.h>
 #include "amdtp.h"
 
@@ -105,6 +106,61 @@ const unsigned int amdtp_syt_intervals[CIP_SFC_COUNT] = {
 EXPORT_SYMBOL(amdtp_syt_intervals);
 
 /**
+ * amdtp_stream_add_pcm_hw_constraints - add hw constraints for PCM substream
+ * @s:          the AMDTP stream, which must be initialized.
+ * @runtime:    the PCM substream runtime
+ */
+int amdtp_stream_add_pcm_hw_constraints(struct amdtp_stream *s,
+                                        struct snd_pcm_runtime *runtime)
+{
+        int err;
+
+        /* AM824 in IEC 61883-6 can deliver 24bit data */
+        err = snd_pcm_hw_constraint_msbits(runtime, 0, 32, 24);
+        if (err < 0)
+                goto end;
+
+        /*
+         * Currently firewire-lib processes 16 packets in one software
+         * interrupt callback. This equals to 2msec but actually the
+         * interval of the interrupts has a jitter.
+         * Additionally, even if adding a constraint to fit period size to
+         * 2msec, actual calculated frames per period doesn't equal to 2msec,
+         * depending on sampling rate.
+         * Anyway, the interval to call snd_pcm_period_elapsed() cannot 2msec.
+         * Here let us use 5msec for safe period interrupt.
+         */
+        err = snd_pcm_hw_constraint_minmax(runtime,
+                                           SNDRV_PCM_HW_PARAM_PERIOD_TIME,
+                                           5000, UINT_MAX);
+        if (err < 0)
+                goto end;
+
+        /* Non-Blocking stream has no more constraints */
+        if (!(s->flags & CIP_BLOCKING))
+                goto end;
+
+        /*
+         * One AMDTP packet can include some frames. In blocking mode, the
+         * number equals to SYT_INTERVAL. So the number is 8, 16 or 32,
+         * depending on its sampling rate. For accurate period interrupt, it's
+         * preferrable to aligh period/buffer sizes to current SYT_INTERVAL.
+         *
+         * TODO: These constraints can be improved with propper rules.
+         * Currently apply LCM of SYT_INTEVALs.
+         */
+        err = snd_pcm_hw_constraint_step(runtime, 0,
+                                         SNDRV_PCM_HW_PARAM_PERIOD_SIZE, 32);
+        if (err < 0)
+                goto end;
+        err = snd_pcm_hw_constraint_step(runtime, 0,
+                                         SNDRV_PCM_HW_PARAM_BUFFER_SIZE, 32);
+end:
+        return err;
+}
+EXPORT_SYMBOL(amdtp_stream_add_pcm_hw_constraints);
+
+/**
  * amdtp_stream_set_parameters - set stream parameters
  * @s: the AMDTP stream to configure
  * @rate: the sample rate
diff --git a/sound/firewire/amdtp.h b/sound/firewire/amdtp.h
index db60425f2781..d6bb7eb86f0f 100644
--- a/sound/firewire/amdtp.h
+++ b/sound/firewire/amdtp.h
@@ -64,6 +64,7 @@ enum cip_sfc {
 struct fw_unit;
 struct fw_iso_context;
 struct snd_pcm_substream;
+struct snd_pcm_runtime;
 struct snd_rawmidi_substream;
 
 enum amdtp_stream_direction {
@@ -130,6 +131,8 @@ int amdtp_stream_start(struct amdtp_stream *s, int channel, int speed);
 void amdtp_stream_update(struct amdtp_stream *s);
 void amdtp_stream_stop(struct amdtp_stream *s);
 
+int amdtp_stream_add_pcm_hw_constraints(struct amdtp_stream *s,
+                                        struct snd_pcm_runtime *runtime);
 void amdtp_stream_set_pcm_format(struct amdtp_stream *s,
                                  snd_pcm_format_t format);
 void amdtp_stream_pcm_prepare(struct amdtp_stream *s);
diff --git a/sound/firewire/dice.c b/sound/firewire/dice.c
index cd4c6b6d072e..a9a30c0161f1 100644
--- a/sound/firewire/dice.c
+++ b/sound/firewire/dice.c
@@ -420,22 +420,7 @@ static int dice_open(struct snd_pcm_substream *substream)
         if (err < 0)
                 goto err_lock;
 
-        err = snd_pcm_hw_constraint_step(runtime, 0,
-                                         SNDRV_PCM_HW_PARAM_PERIOD_SIZE, 32);
-        if (err < 0)
-                goto err_lock;
-        err = snd_pcm_hw_constraint_step(runtime, 0,
-                                         SNDRV_PCM_HW_PARAM_BUFFER_SIZE, 32);
-        if (err < 0)
-                goto err_lock;
-
-        err = snd_pcm_hw_constraint_minmax(runtime,
-                                           SNDRV_PCM_HW_PARAM_PERIOD_TIME,
-                                           5000, UINT_MAX);
-        if (err < 0)
-                goto err_lock;
-
-        err = snd_pcm_hw_constraint_msbits(runtime, 0, 32, 24);
+        err = amdtp_stream_add_pcm_hw_constraints(&dice->stream, runtime);
         if (err < 0)
                 goto err_lock;
 
diff --git a/sound/firewire/speakers.c b/sound/firewire/speakers.c
index c07e7cd154f2..58e7ab010c60 100644
--- a/sound/firewire/speakers.c
+++ b/sound/firewire/speakers.c
@@ -167,13 +167,7 @@ static int fwspk_open(struct snd_pcm_substream *substream)
         if (err < 0)
                 return err;
 
-        err = snd_pcm_hw_constraint_minmax(runtime,
-                                           SNDRV_PCM_HW_PARAM_PERIOD_TIME,
-                                           5000, UINT_MAX);
-        if (err < 0)
-                return err;
-
-        err = snd_pcm_hw_constraint_msbits(runtime, 0, 32, 24);
+        err = amdtp_stream_add_pcm_hw_constraints(&fwspk->stream, runtime);
         if (err < 0)
                 return err;