diff options
Diffstat (limited to 'target/linux/brcm2708/patches-4.19/950-0135-bcm2835-interpolate-audio-delay.patch')
| -rw-r--r-- | target/linux/brcm2708/patches-4.19/950-0135-bcm2835-interpolate-audio-delay.patch | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/target/linux/brcm2708/patches-4.19/950-0135-bcm2835-interpolate-audio-delay.patch b/target/linux/brcm2708/patches-4.19/950-0135-bcm2835-interpolate-audio-delay.patch new file mode 100644 index 0000000000..55cd26b25b --- /dev/null +++ b/target/linux/brcm2708/patches-4.19/950-0135-bcm2835-interpolate-audio-delay.patch @@ -0,0 +1,89 @@ +From 652b0ec2ab2d2e2af7bb4f7d62a4020a20720677 Mon Sep 17 00:00:00 2001 +From: wm4 <wm4@nowhere> +Date: Wed, 13 Jan 2016 19:44:47 +0100 +Subject: [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 | 12 +++++++++++- + .../staging/vc04_services/bcm2835-audio/bcm2835.h | 1 + + 2 files changed, 12 insertions(+), 1 deletion(-) + +--- a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c ++++ b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c +@@ -11,7 +11,7 @@ + /* 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, +@@ -81,6 +81,8 @@ void bcm2835_playback_fifo(struct bcm283 + 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); +@@ -306,6 +308,7 @@ static int snd_bcm2835_pcm_prepare(struc + 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, +@@ -397,12 +400,19 @@ snd_bcm2835_pcm_pointer(struct snd_pcm_s + { + 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); +--- a/drivers/staging/vc04_services/bcm2835-audio/bcm2835.h ++++ b/drivers/staging/vc04_services/bcm2835-audio/bcm2835.h +@@ -133,6 +133,7 @@ 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; |