Subject: [PATCH 075/104] ALSA: pcm - add support for hostless audio

Allow some PCM devices to be hostless, i.e. there is no PCM data transferred
to or from the host CPU. This can be used to minimise power on systems since
the CPU can idle/sleep during the PCM device operation (e.g. a phone call
where the DAI is between a MODEM and DSP)

TODO: cleanup, look at adding a read/write blocker.

Singed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>

3 files changed, 5 insertions, 0 deletions

diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index e1bad113061..6a187658e8f 100644
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -413,6 +413,7 @@ struct snd_pcm_substream {
 #endif
         /* misc flags */
         unsigned int hw_opened: 1;
+        unsigned int hw_no_buffer: 1; /* substream may not have a buffer */
 };
 
 #define SUBSTREAM_BUSY(substream) ((substream)->ref_count > 0)
diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index 33884426a64..cd69b38622b 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -1961,6 +1961,9 @@ static int pcm_sanity_check(struct snd_pcm_substream *substream)
         struct snd_pcm_runtime *runtime;
         if (PCM_RUNTIME_CHECK(substream))
                 return -ENXIO;
+        /* TODO: consider and -EINVAL here */
+        if (substream->hw_no_buffer)
+                snd_printd("%s: warning this PCM is host less\n", __func__);
         runtime = substream->runtime;
         if (snd_BUG_ON(!substream->ops->copy && !runtime->dma_area))
                 return -EINVAL;
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 1c6be91dfb9..c6698efb44c 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -842,6 +842,7 @@ static int snd_pcm_pre_start(struct snd_pcm_substream *substream, int state)
         if (runtime->status->state != SNDRV_PCM_STATE_PREPARED)
                 return -EBADFD;
         if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&
+            !substream->hw_no_buffer &&
             !snd_pcm_playback_data(substream))
                 return -EPIPE;
         runtime->trigger_master = substream;