ALSA: core: selection of audio_tstamp type and accuracy reports

Audio timestamps can be extracted from sample counters, wall clocks,
PHC clocks (Ethernet AVB), on-demand synchronized snapshots. This
patch provides the ability to report timestamping capabilities, select
timestamp types and retrieve timestamp accuracy, if supported.
Details can be found in Documentations/sound/alsa/timestamping.txt

This functionality is introduced by reclaiming the reserved_aligned
field introduced by commit9c7066aef4a5eb8e4063de28f06c508bf6f2963a
in snd_pcm_status to provide userspace with selection/query capabilities.
Additional driver_tstamp and audio_tstamp_accuracy fields are also added.

snd_pcm_mmap_status remains a read-only structure with only
the audio timestamp value accessible from user space. The selection
of audio timestamp type is done through snd_pcm_status only

This commit does not impact ABI and does not impact the default
behavior. By default audio timestamp is aligned with hw_pointer and
reports the DMA position. Backwards compatibility is handled by using
the HDAudio wall clock for playback and the hw_ptr for all other
cases.

For timestamp selection a new STATUS_EXT ioctl is introduced with
read/write parameters. Alsa-lib will be modified to make use of
STATUS_EXT.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 60 insertions, 0 deletions

diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index c0ddb7e69c28..60f0e48f7905 100644
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -60,6 +60,9 @@ struct snd_pcm_hardware {
 
 struct snd_pcm_substream;
 
+struct snd_pcm_audio_tstamp_config; /* definitions further down */
+struct snd_pcm_audio_tstamp_report;
+
 struct snd_pcm_ops {
 	int (*open)(struct snd_pcm_substream *substream);
 	int (*close)(struct snd_pcm_substream *substream);
@@ -281,6 +284,58 @@ struct snd_pcm_hw_constraint_ranges {
 
 struct snd_pcm_hwptr_log;
 
+/*
+ * userspace-provided audio timestamp config to kernel,
+ * structure is for internal use only and filled with dedicated unpack routine
+ */
+struct snd_pcm_audio_tstamp_config {
+	/* 5 of max 16 bits used */
+	u32 type_requested:4;
+	u32 report_delay:1; /* add total delay to A/D or D/A */
+};
+
+static inline void snd_pcm_unpack_audio_tstamp_config(__u32 data,
+						struct snd_pcm_audio_tstamp_config *config)
+{
+	config->type_requested = data & 0xF;
+	config->report_delay = (data >> 4) & 1;
+}
+
+/*
+ * kernel-provided audio timestamp report to user-space
+ * structure is for internal use only and read by dedicated pack routine
+ */
+struct snd_pcm_audio_tstamp_report {
+	/* 6 of max 16 bits used for bit-fields */
+
+	/* for backwards compatibility */
+	u32 valid:1;
+
+	/* actual type if hardware could not support requested timestamp */
+	u32 actual_type:4;
+
+	/* accuracy represented in ns units */
+	u32 accuracy_report:1; /* 0 if accuracy unknown, 1 if accuracy field is valid */
+	u32 accuracy; /* up to 4.29s, will be packed in separate field  */
+};
+
+static inline void snd_pcm_pack_audio_tstamp_report(__u32 *data, __u32 *accuracy,
+						const struct snd_pcm_audio_tstamp_report *report)
+{
+	u32 tmp;
+
+	tmp = report->accuracy_report;
+	tmp <<= 4;
+	tmp |= report->actual_type;
+	tmp <<= 1;
+	tmp |= report->valid;
+
+	*data &= 0xffff; /* zero-clear MSBs */
+	*data |= (tmp << 16);
+	*accuracy = report->accuracy;
+}
+
+
 struct snd_pcm_runtime {
 	/* -- Status -- */
 	struct snd_pcm_substream *trigger_master;
@@ -361,6 +416,11 @@ struct snd_pcm_runtime {
 
 	struct snd_dma_buffer *dma_buffer_p;	/* allocated buffer */
 
+	/* -- audio timestamp config -- */
+	struct snd_pcm_audio_tstamp_config audio_tstamp_config;
+	struct snd_pcm_audio_tstamp_report audio_tstamp_report;
+	struct timespec driver_tstamp;
+
 #if defined(CONFIG_SND_PCM_OSS) || defined(CONFIG_SND_PCM_OSS_MODULE)
 	/* -- OSS things -- */
 	struct snd_pcm_oss_runtime oss;