ALSA: compress_core: Update calc_avail to use cumulative values

The app_pointer is managed locally by the compress core for memory
mapped DSPs but for DSPs that are not memory mapped this would have to
be manually updated from within the DSP driver itself, which is hardly
very idiomatic.

This patch switches to using the cumulative values to calculate the
available buffer space because these are already gracefully passed out
of the DSP driver to the compress core and otherwise should be
functionally equivalent.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Richard Fitzgerald <rf@opensource.wolfsonmicro.com>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/compress_offload.c

@@ -160,8 +160,6 @@ static int snd_compr_update_tstamp(struct snd_compr_stream *stream,
 static size_t snd_compr_calc_avail(struct snd_compr_stream *stream,
 		struct snd_compr_avail *avail)
 {
-	long avail_calc; /*this needs to be signed variable */
-
 	memset(avail, 0, sizeof(*avail));
 	snd_compr_update_tstamp(stream, &avail->tstamp);
 	/* Still need to return avail even if tstamp can't be filled in */
@@ -184,22 +182,11 @@ static size_t snd_compr_calc_avail(struct snd_compr_stream *stream,
 		return stream->runtime->buffer_size;
 	}
 
-	/* FIXME: this routine isn't consistent, in one test we use
-	 * cumulative values and in the other byte offsets. Do we
-	 * really need the byte offsets if the cumulative values have
-	 * been updated? In the PCM interface app_ptr and hw_ptr are
-	 * already cumulative */
-
-	avail_calc = stream->runtime->buffer_size -
-		(stream->runtime->app_pointer - stream->runtime->hw_pointer);
-	pr_debug("calc avail as %ld, app_ptr %lld, hw+ptr %lld\n", avail_calc,
-			stream->runtime->app_pointer,
-			stream->runtime->hw_pointer);
-	if (avail_calc >= stream->runtime->buffer_size)
-		avail_calc -= stream->runtime->buffer_size;
-	pr_debug("ret avail as %ld\n", avail_calc);
-	avail->avail = avail_calc;
-	return avail_calc;
+	avail->avail = stream->runtime->buffer_size -
+		(stream->runtime->total_bytes_available -
+		 stream->runtime->total_bytes_transferred);
+	pr_debug("ret avail as %lld\n", avail->avail);
+	return avail->avail;
 }
 
 static inline size_t snd_compr_get_avail(struct snd_compr_stream *stream)