ASoC: SOF: Intel: power optimizations with HDaudio SPIB register

Merge series from Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>:

	The use of the SPIB register helps reduce power consumption - though
	to a smaller degree than DMI_L1. This hardware capability is however
	incompatible with userspace-initiated rewinds typically used by
	PulseAudio.

	In the past (2015..2017) Intel suggested an API extension to let
	applications disable rewinds. At the time the feedback was that such a
	capability was too Intel-specific and SPIB remained unused except for
	loading DSP code. We now see devices with smaller batteries being
	released, and it's time to revisit Linux support for SPIB to extend
	battery life.

	In this update the rewinds are disabled via an opt-in kernel
	parameter. In the previous reviews, there was consensus that a Kconfig
	option was too complicated for distributions to set, and we are
	missing a TBD API to expose such capabilities to user-space.

	The debate on whether or not to use rewinds, and the impact of
	disabling rewinds, will likely be closed when Intel releases the
	'deep-buffer' support, currently under development [2][3]. With this
	solution, rewinds will not be needed, ever. When an application deals
	with content that is not latency-sensitive (e.g. music playback), it
	will be able to reduce power consumption by selecting a different PCM
	device with increased buffering capabilities.  Low-latency streams
	will be handled by the 'regular' path. In other words, the impossible
	compromise between power and latency will be handled with different
	PCM devices/profiles for the same endpoint, and we can push the design
	of capability negotiation to a later time when all the building blocks
	(firmware topology, kernel, userspace) are ready - we still have
	firmware xruns, DPCM race conditions to solve, and a need to describe
	these alternate PCM devices with UCM using 'modifiers'.

1 files changed, 9 insertions, 0 deletions

diff --git a/sound/soc/sof/pcm.c b/sound/soc/sof/pcm.c
index 0ceb1a9cbf73..1bf7e60be772 100644
--- a/sound/soc/sof/pcm.c
+++ b/sound/soc/sof/pcm.c
@@ -916,6 +916,14 @@ static void sof_pcm_remove(struct snd_soc_component *component)
 	snd_soc_tplg_component_remove(component);
 }
 
+static int sof_pcm_ack(struct snd_soc_component *component,
+		       struct snd_pcm_substream *substream)
+{
+	struct snd_sof_dev *sdev = snd_soc_component_get_drvdata(component);
+
+	return snd_sof_pcm_platform_ack(sdev, substream);
+}
+
 void snd_sof_new_platform_drv(struct snd_sof_dev *sdev)
 {
 	struct snd_soc_component_driver *pd = &sdev->plat_drv;
@@ -934,6 +942,7 @@ void snd_sof_new_platform_drv(struct snd_sof_dev *sdev)
 	pd->hw_free = sof_pcm_hw_free;
 	pd->trigger = sof_pcm_trigger;
 	pd->pointer = sof_pcm_pointer;
+	pd->ack = sof_pcm_ack;
 
 #if IS_ENABLED(CONFIG_SND_SOC_SOF_DEBUG_PROBES)
 	pd->compress_ops = &sof_probe_compressed_ops;