From 7b2d99fa6b127707cf0d78feedbb3613aed4d576 Mon Sep 17 00:00:00 2001 From: Takashi Sakamoto Date: Fri, 25 Apr 2014 22:44:52 +0900 Subject: 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 Signed-off-by: Takashi Iwai --- sound/firewire/amdtp.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 56 insertions(+) (limited to 'sound/firewire/amdtp.c') 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 #include #include +#include #include #include "amdtp.h" @@ -104,6 +105,61 @@ 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 -- cgit v1.2.1