From: Nick Stoughton Subject: [RFC] ALSA: provide a simple mechanism to start playback at a given time Date: Tue, 14 Oct 2014 10:29:31 +0200 Message-ID: <543d33f8.4a66b40a.638d.0583@mx.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-wg0-f51.google.com (mail-wg0-f51.google.com [74.125.82.51]) by alsa0.perex.cz (Postfix) with ESMTP id 20B772606B9 for ; Tue, 14 Oct 2014 16:32:30 +0200 (CEST) Received: by mail-wg0-f51.google.com with SMTP id b13so10852645wgh.34 for ; Tue, 14 Oct 2014 07:32:25 -0700 (PDT) Received: from nstoughton@aether.com ([62.156.150.204]) by mx.google.com with ESMTPSA id fm10sm8261889wib.21.2014.10.14.07.32.23 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 14 Oct 2014 07:32:24 -0700 (PDT) List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: alsa-devel-bounces@alsa-project.org To: alsa-devel@alsa-project.org List-Id: alsa-devel@alsa-project.org Initial implementation / Request For Comment. Given an absolute time based on a given clock (CLOCK_MONOTONIC, CLOCK_MONOTONIC_RAW, CLOCK_REALTIME etc), setup a high resolution timer to cause playback to be triggered at that time. --- include/linux/timekeeping.h | 3 ++ include/uapi/sound/asound.h | 6 +++ kernel/time/timekeeping.c | 16 ++++++++ sound/core/pcm_native.c | 99 +++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 124 insertions(+) diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h index 1caa6b0..74eb6b2 100644 --- a/include/linux/timekeeping.h +++ b/include/linux/timekeeping.h @@ -32,6 +32,9 @@ extern void ktime_get_ts64(struct timespec64 *ts); extern int __getnstimeofday64(struct timespec64 *tv); extern void getnstimeofday64(struct timespec64 *tv); +/* Get the offset between monotonic and monotonic raw clocks */ +extern ktime_t ktime_get_raw_offset(void); + #if BITS_PER_LONG == 64 static inline int __getnstimeofday(struct timespec *ts) { diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h index 6ee5867..c7aa88c 100644 --- a/include/uapi/sound/asound.h +++ b/include/uapi/sound/asound.h @@ -462,6 +462,11 @@ struct snd_xfern { snd_pcm_uframes_t frames; }; +struct snd_clock_time { + clockid_t clock; + struct timespec time; +}; + enum { SNDRV_PCM_TSTAMP_TYPE_GETTIMEOFDAY = 0, /* gettimeofday equivalent */ SNDRV_PCM_TSTAMP_TYPE_MONOTONIC, /* posix_clock_monotonic equivalent */ @@ -547,6 +552,7 @@ enum { #define SNDRV_PCM_IOCTL_READN_FRAMES _IOR('A', 0x53, struct snd_xfern) #define SNDRV_PCM_IOCTL_LINK _IOW('A', 0x60, int) #define SNDRV_PCM_IOCTL_UNLINK _IO('A', 0x61) +#define SNDRV_PCM_IOCTL_START_AT _IOR('A', 0x62, struct snd_clock_time) /***************************************************************************** * * diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index ec1791f..3d5d0bc 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -789,6 +789,22 @@ error: /* even if we error out, we forwarded the time, so call update */ } EXPORT_SYMBOL(timekeeping_inject_offset); +/** + * ktime_get_raw_offset - get the offset in ktime format between + * the monotonic_raw clock and the monotonic clock + */ +ktime_t ktime_get_raw_offset(void) +{ + struct timespec rawtime = {0,0}; + struct timespec now = {0,0}; + struct timespec delta; + + ktime_get_ts(&now); + getrawmonotonic(&rawtime); + delta = timespec_sub(now, rawtime); + return timespec_to_ktime(delta); +} +EXPORT_SYMBOL(ktime_get_raw_offset); /** * timekeeping_get_tai_offset - Returns current TAI offset from UTC diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c index 85fe1a2..1121127 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -27,6 +27,7 @@ #include #include #include +#include #include #include #include @@ -38,6 +39,9 @@ #if defined(CONFIG_MIPS) && defined(CONFIG_DMA_NONCOHERENT) #include #endif +#if defined(CONFIG_HIGH_RES_TIMERS) +#include +#endif /* * Compatibility @@ -1016,6 +1020,99 @@ static struct action_ops snd_pcm_action_start = { .post_action = snd_pcm_post_start }; +#ifdef CONFIG_HIGH_RES_TIMERS +/* + * hrtimer interface + */ + +struct hrtimer_pcm { + struct hrtimer timer; + struct snd_pcm_substream *substream; +}; + +/* + * called from a hard irq context - no need for locks. + * only problem is that the caller might have gone away and closed the substream + * before the timer expires. + */ +enum hrtimer_restart snd_pcm_do_start_time(struct hrtimer *timer) +{ + struct hrtimer_pcm *pcm_timer; + struct snd_pcm_substream *substream; + int ret; + + pcm_timer = container_of(timer, struct hrtimer_pcm, timer); + substream = pcm_timer->substream; + + if (substream->runtime) { + ret = snd_pcm_do_start(substream, SNDRV_PCM_STATE_RUNNING); + if (ret == 0) { + snd_pcm_post_start(substream, SNDRV_PCM_STATE_RUNNING); + } + } + kfree(pcm_timer); + + return HRTIMER_NORESTART; +} + +int snd_pcm_start_at(struct snd_pcm_substream *substream, + struct snd_clock_time __user *_start_time) +{ + struct hrtimer_pcm *pcm_timer; + struct snd_clock_time start_time; + int clock; + ktime_t start_kt; + ktime_t raw_offset; + int ret; + + if (copy_from_user(&start_time, _start_time, sizeof(start_time))) + return -EFAULT; + + if (!timespec_valid(&start_time.time)) + return -EINVAL; + + start_kt = timespec_to_ktime(start_time.time); + clock = start_time.clock; + if (start_time.clock == CLOCK_MONOTONIC_RAW) { + raw_offset = ktime_get_raw_offset(); + + /* convert to clock monotonic */ + start_kt = ktime_add(raw_offset, start_kt); + clock = CLOCK_MONOTONIC; + } + + /* if not playback substream or less than 100 ms give up */ + if (substream->stream != SNDRV_PCM_STREAM_PLAYBACK || + (ktime_compare(start_kt, ktime_add_ns(ktime_get(), 100000000)) <= 0)) { + return snd_pcm_action_lock_irq(&snd_pcm_action_start, + substream, SNDRV_PCM_STATE_RUNNING); + } + + ret = snd_pcm_pre_start(substream, SNDRV_PCM_STATE_PREPARED); + if (ret != 0) { + return ret; + } + + pcm_timer = kmalloc(sizeof(*pcm_timer), GFP_KERNEL); + hrtimer_init(&pcm_timer->timer, clock, HRTIMER_MODE_ABS); + + pcm_timer->timer.function = snd_pcm_do_start_time; + pcm_timer->substream = substream; + + hrtimer_start(&pcm_timer->timer, start_kt, HRTIMER_MODE_ABS); + + return 0; +} +#else +/* without high res time, interface is identical to snd_pcm_start() */ +int snd_pcm_start_at(struct snd_pcm_substream *substream, + struct snd_clock_time __user *_start_time) +{ + return snd_pcm_action_lock_irq(&snd_pcm_action_start, + substream, SNDRV_PCM_STATE_RUNNING); +} +#endif + /** * snd_pcm_start - start all linked streams * @substream: the PCM substream instance @@ -2698,6 +2795,8 @@ static int snd_pcm_common_ioctl1(struct file *file, return snd_pcm_reset(substream); case SNDRV_PCM_IOCTL_START: return snd_pcm_action_lock_irq(&snd_pcm_action_start, substream, SNDRV_PCM_STATE_RUNNING); + case SNDRV_PCM_IOCTL_START_AT: + return snd_pcm_start_at(substream, arg); case SNDRV_PCM_IOCTL_LINK: return snd_pcm_link(substream, (int)(unsigned long) arg); case SNDRV_PCM_IOCTL_UNLINK: -- 1.9.3