pcm: plug - add automatic conversion for iec958 subframe samples

As Pavel noted, a possibility to automatically convert standard
linear samples to iec958 subframe format would be handy for latest
Raspberry HDMI driver.

Link: https://lore.kernel.org/alsa-devel/[email protected]/
Suggested-by: Pavel Hofman <[email protected]>
Signed-off-by: Jaroslav Kysela <[email protected]>

configure.ac

@@ -642,6 +642,9 @@ fi
 if test "$build_pcm_alaw" = "yes"; then
   AC_DEFINE([BUILD_PCM_PLUGIN_ALAW], "1", [Build PCM alaw plugin])
 fi
+if test "$build_pcm_iec958" = "yes"; then
+  AC_DEFINE([BUILD_PCM_PLUGIN_IEC958], "1", [Build PCM iec958 plugin])
+fi
 if test "$build_pcm_mmap_emul" = "yes"; then
   AC_DEFINE([BUILD_PCM_PLUGIN_MMAP_EMUL], "1", [Build PCM mmap-emul plugin])
 fi

include/pcm_plugin.h

@@ -133,6 +133,19 @@ int _snd_pcm_adpcm_open(snd_pcm_t **pcmp, const char *name,
 			snd_config_t *root, snd_config_t *conf,
 			snd_pcm_stream_t stream, int mode);
 
+/*
+ *  IEC958 subframe conversion plugin
+ */
+int snd_pcm_iec958_open(snd_pcm_t **pcmp, const char *name,
+			snd_pcm_format_t sformat, snd_pcm_t *slave,
+			int close_slave,
+			const unsigned char *status_bits,
+			const unsigned char *preamble_vals,
+			int hdmi_mode);
+int _snd_pcm_iec958_open(snd_pcm_t **pcmp, const char *name,
+			 snd_config_t *root, snd_config_t *conf,
+			 snd_pcm_stream_t stream, int mode);
+
 /*
  *  Route plugin for linear formats
  */

src/pcm/pcm_plug.c

@@ -186,7 +186,8 @@ static const snd_pcm_format_t linear_preferred_formats[] = {
 
 #if defined(BUILD_PCM_PLUGIN_MULAW) || \
 	defined(BUILD_PCM_PLUGIN_ALAW) || \
-	defined(BUILD_PCM_PLUGIN_ADPCM)
+	defined(BUILD_PCM_PLUGIN_ADPCM) || \
+	defined(BUILD_PCM_PLUGIN_IEC958)
 #define BUILD_PCM_NONLINEAR
 #endif
 
@@ -201,6 +202,10 @@ static const snd_pcm_format_t nonlinear_preferred_formats[] = {
 #ifdef BUILD_PCM_PLUGIN_ADPCM
 	SND_PCM_FORMAT_IMA_ADPCM,
 #endif
+#ifdef BUILD_PCM_PLUGIN_IEC958
+	SND_PCM_FORMAT_IEC958_SUBFRAME_LE,
+	SND_PCM_FORMAT_IEC958_SUBFRAME_BE,
+#endif
 };
 #endif
 
@@ -490,6 +495,18 @@ static int snd_pcm_plug_change_channels(snd_pcm_t *pcm, snd_pcm_t **new, snd_pcm
 }
 #endif
 
+#ifdef BUILD_PCM_PLUGIN_IEC958
+static int iec958_open(snd_pcm_t **pcmp, const char *name,
+		       snd_pcm_format_t sformat, snd_pcm_t *slave,
+		       int close_slave)
+{
+	unsigned char preamble_vals[3] = {
+		0x08, 0x02, 0x04 /* Z, X, Y */
+	};
+	return snd_pcm_iec958_open(pcmp, name, sformat, slave, close_slave, NULL, preamble_vals, 0);
+}
+#endif
+
 static int snd_pcm_plug_change_format(snd_pcm_t *pcm, snd_pcm_t **new, snd_pcm_plug_params_t *clt, snd_pcm_plug_params_t *slv)
 {
 	snd_pcm_plug_t *plug = pcm->private_data;
@@ -526,6 +543,12 @@ static int snd_pcm_plug_change_format(snd_pcm_t *pcm, snd_pcm_t **new, snd_pcm_p
 		case SND_PCM_FORMAT_IMA_ADPCM:
 			f = snd_pcm_adpcm_open;
 			break;
+#endif
+#ifdef BUILD_PCM_PLUGIN_IEC958
+		case SND_PCM_FORMAT_IEC958_SUBFRAME_LE:
+		case SND_PCM_FORMAT_IEC958_SUBFRAME_BE:
+			f = iec958_open;
+			break;
 #endif
 		default:
 #ifdef BUILD_PCM_PLUGIN_LFLOAT
@@ -566,6 +589,12 @@ static int snd_pcm_plug_change_format(snd_pcm_t *pcm, snd_pcm_t **new, snd_pcm_p
 		case SND_PCM_FORMAT_IMA_ADPCM:
 			f = snd_pcm_adpcm_open;
 			break;
+#endif
+#ifdef BUILD_PCM_PLUGIN_IEC958
+		case SND_PCM_FORMAT_IEC958_SUBFRAME_LE:
+		case SND_PCM_FORMAT_IEC958_SUBFRAME_BE:
+			f = iec958_open;
+			break;
 #endif
 		default:
 			return -EINVAL;