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ALSA: firewire-lib: tune the maximum available size of PCM period

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Linux driver for 1394 OHCI controller voluntarily flushes isoc context
when total size of accumulated context header reached PAGE_SIZE. This
kicks tasklet for the isoc context. This is inconvenient to process
runtime of PCM substream.

This commit adds a restriction of the maximum size of PCM period to
avoid this behaviour.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20191017155424.885-12-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Sakamoto 2019-10-18 00:54:23 +09:00 committed by Takashi Iwai
parent e229853d50
commit 99921ec67d
1 changed files with 18 additions and 11 deletions
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29
sound/firewire/amdtp-stream.c
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@ -176,6 +176,8 @@ int amdtp_stream_add_pcm_hw_constraints(struct amdtp_stream *s,
struct snd_pcm_runtime *runtime)
{
struct snd_pcm_hardware *hw = &runtime->hw;
unsigned int ctx_header_size;
unsigned int maximum_usec_per_period;
int err;
hw->info = SNDRV_PCM_INFO_BATCH |
@ -196,19 +198,24 @@ int amdtp_stream_add_pcm_hw_constraints(struct amdtp_stream *s,
hw->period_bytes_max = hw->period_bytes_min * 2048;
hw->buffer_bytes_max = hw->period_bytes_max * hw->periods_min;
/*
* 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.
*/
// Linux driver for 1394 OHCI controller voluntarily flushes isoc
// context when total size of accumulated context header reaches
// PAGE_SIZE. This kicks tasklet for the isoc context and brings
// callback in the middle of scheduled interrupts.
// Although AMDTP streams in the same domain use the same events per
// IRQ, use the largest size of context header between IT/IR contexts.
// Here, use the value of context header in IR context is for both
// contexts.
if (!(s->flags & CIP_NO_HEADER))
ctx_header_size = IR_CTX_HEADER_SIZE_CIP;
else
ctx_header_size = IR_CTX_HEADER_SIZE_NO_CIP;
maximum_usec_per_period = USEC_PER_SEC * PAGE_SIZE /
CYCLES_PER_SECOND / ctx_header_size;
err = snd_pcm_hw_constraint_minmax(runtime,
SNDRV_PCM_HW_PARAM_PERIOD_TIME,
5000, UINT_MAX);
5000, maximum_usec_per_period);
if (err < 0)
goto end;