Messages in this thread Patch in this message | | | Subject | Re: [PATCH 17/29] staging: bcm2835-audio: Add 10ms period constraint | From | Stefan Wahren <> | Date | Wed, 19 Sep 2018 11:42:22 +0200 |
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Hi Takashi,
Am 04.09.2018 um 17:58 schrieb Takashi Iwai: > It seems that the resolution of vc04 callback is in 10 msec; i.e. the > minimal period size is also 10 msec. > > This patch adds the corresponding hw constraint. > > Signed-off-by: Takashi Iwai <tiwai@suse.de> > --- > drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c > index 9659c25b9f9d..6d89db6e14e4 100644 > --- a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c > +++ b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c > @@ -145,6 +145,11 @@ static int snd_bcm2835_playback_open_generic( > SNDRV_PCM_HW_PARAM_PERIOD_BYTES, > 16); > > + /* position update is in 10ms order */ > + snd_pcm_hw_constraint_minmax(runtime, > + SNDRV_PCM_HW_PARAM_PERIOD_TIME, > + 10 * 1000, UINT_MAX); > + > chip->alsa_stream[idx] = alsa_stream; > > chip->opened |= (1 << idx);
in the Foundation Kernel (Downstream) there is a patch to interpolate the audio delay. So my questions is, does your patch above makes the following patch obsolete?
[PATCH] bcm2835: interpolate audio delay
It appears the GPU only sends us a message all 10ms to update the playback progress. Other than this, the playback position (what SNDRV_PCM_IOCTL_DELAY will return) is not updated at all. Userspace will see jitter up to 10ms in the audio position.
Make this a bit nicer for userspace by interpolating the position using the CPU clock.
I'm not sure if setting snd_pcm_runtime.delay is the right approach for this. Or if there is maybe an already existing mechanism for position interpolation in the ALSA core.
I only set SNDRV_PCM_INFO_BATCH because this appears to remove at least one situation snd_pcm_runtime.delay is used, so I have to worry less in which place I have to update this field, or how it interacts with the rest of ALSA.
In the future, it might be nice to use VC_AUDIO_MSG_TYPE_LATENCY. One problem is that it requires sending a videocore message, and waiting for a reply, which could make the implementation much harder due to locking and synchronization requirements. --- .../vc04_services/bcm2835-audio/bcm2835-pcm.c | 13 +++++++++++-- .../staging/vc04_services/bcm2835-audio/bcm2835.h | 1 + 2 files changed, 12 insertions(+), 2 deletions(-)
diff --git a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c index 94654c0c7bba5..36165a60fb059 100644 --- a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c +++ b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c @@ -22,7 +22,7 @@ /* hardware definition */ static const struct snd_pcm_hardware snd_bcm2835_playback_hw = { .info = (SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_BLOCK_TRANSFER | - SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID), + SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID | SNDRV_PCM_INFO_BATCH), .formats = SNDRV_PCM_FMTBIT_U8 | SNDRV_PCM_FMTBIT_S16_LE, .rates = SNDRV_PCM_RATE_CONTINUOUS | SNDRV_PCM_RATE_8000_48000, .rate_min = 8000, @@ -93,6 +93,8 @@ void bcm2835_playback_fifo(struct bcm2835_alsa_stream *alsa_stream) alsa_stream->pos %= alsa_stream->buffer_size; } + alsa_stream->interpolate_start = ktime_get_ns(); + if (alsa_stream->substream) { if (new_period) snd_pcm_period_elapsed(alsa_stream->substream); @@ -323,6 +325,7 @@ static int snd_bcm2835_pcm_prepare(struct snd_pcm_substream *substream) alsa_stream->buffer_size = snd_pcm_lib_buffer_bytes(substream); alsa_stream->period_size = snd_pcm_lib_period_bytes(substream); alsa_stream->pos = 0; + alsa_stream->interpolate_start = ktime_get_ns(); audio_debug("buffer_size=%d, period_size=%d pos=%d frame_bits=%d\n", alsa_stream->buffer_size, alsa_stream->period_size, @@ -415,13 +418,19 @@ snd_bcm2835_pcm_pointer(struct snd_pcm_substream *substream) { struct snd_pcm_runtime *runtime = substream->runtime; struct bcm2835_alsa_stream *alsa_stream = runtime->private_data; - + u64 now = ktime_get_ns(); audio_debug("pcm_pointer... (%d) hwptr=%d appl=%d pos=%d\n", 0, frames_to_bytes(runtime, runtime->status->hw_ptr), frames_to_bytes(runtime, runtime->control->appl_ptr), alsa_stream->pos); + /* Give userspace better delay reporting by interpolating between GPU + * notifications, assuming audio speed is close enough to the clock + * used for ktime */ + if (alsa_stream->interpolate_start && alsa_stream->interpolate_start < now) + runtime->delay = -(int)div_u64((now - alsa_stream->interpolate_start) * runtime->rate, 1000000000); + return snd_pcm_indirect_playback_pointer(substream, &alsa_stream->pcm_indirect, alsa_stream->pos); diff --git a/drivers/staging/vc04_services/bcm2835-audio/bcm2835.h b/drivers/staging/vc04_services/bcm2835-audio/bcm2835.h index 379604d3554e8..e64862e1781be 100644 --- a/drivers/staging/vc04_services/bcm2835-audio/bcm2835.h +++ b/drivers/staging/vc04_services/bcm2835-audio/bcm2835.h @@ -137,6 +137,7 @@ struct bcm2835_alsa_stream { unsigned int pos; unsigned int buffer_size; unsigned int period_size; + u64 interpolate_start; atomic_t retrieved; struct bcm2835_audio_instance *instance;
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