V2 of patches to show how the audio wall clock (eg. the HDAudio one) can be used to provide precise audio timestamps and track the drift between audio time and system time. On my laptop I am able to track a 7ppm delta. I will explain in more details how this can be used during LPC in San Diego, but with the summer coming I'd like to get feedback as there are changes to the core/alsa-lib that haven't been modified in years.

TODO: - 64-bit alignment, verification of pcm_compat.c changes - handling of digital inputs, need to disable wall-clock timestamps in that case (feedback from Clemens) - check differences in protocol - change timecounter to avoid accumulation of rounding errors in cycle->ns conversions - check overflows - rework the timecounter init on trigger

Pierre-Louis Bossart (2): ALSA: core: add hooks for audio timestamps read from WALLCLOCK ALSA: hda: support for wallclock timestamps

include/sound/asound.h | 7 ++++- include/sound/pcm.h | 2 + sound/core/pcm_compat.c | 13 +++++++++- sound/core/pcm_lib.c | 15 ++++++++++- sound/core/pcm_native.c | 2 + sound/pci/hda/hda_intel.c | 54 ++++++++++++++++++++++++++++++++++++++++++++- 6 files changed, 86 insertions(+), 7 deletions(-)