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, 1 insertions, 1 deletions

diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
index 5fbb79e30819..ff7e638221c5 100644
--- a/include/uapi/sound/asound.h
+++ b/include/uapi/sound/asound.h
@@ -300,7 +300,7 @@ typedef int __bitwise snd_pcm_subformat_t;
 #define SNDRV_PCM_INFO_HAS_LINK_ESTIMATED_ATIME    0x04000000  /* report estimated link audio time */
 #define SNDRV_PCM_INFO_HAS_LINK_SYNCHRONIZED_ATIME 0x08000000  /* report synchronized audio/system time */
 #define SNDRV_PCM_INFO_EXPLICIT_SYNC	0x10000000	/* needs explicit sync of pointers and data */
-
+#define SNDRV_PCM_INFO_NO_REWINDS	0x20000000	/* hardware can only support monotonic changes of appl_ptr */
 #define SNDRV_PCM_INFO_DRAIN_TRIGGER	0x40000000		/* internal kernel flag - trigger in drain */
 #define SNDRV_PCM_INFO_FIFO_IN_FRAMES	0x80000000	/* internal kernel flag - FIFO size is in frames */