Re: ALSA-LIB: Support for format IEC958_SUBFRAME_LE in the plug plugin?

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On 08. 02. 24 15:40, Jaroslav Kysela wrote:
On 07. 02. 24 16:34, Pavel Hofman wrote:

But honestly I still do not understand what it actually does and what is
the goal of snd_pcm_plug_slave_format().

Without that I cannot modify snd_pcm_plug_slave_format() correctly to
incorporate support for IEC958.

I believe you're looking to a wrong place. Here's incomplete code:

==========
diff --git a/configure.ac b/configure.ac
index 7a152a4a..3f238302 100644
--- a/configure.ac
+++ b/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
diff --git a/include/pcm_plugin.h b/include/pcm_plugin.h
index 2d014394..f3e8f3b5 100644
--- a/include/pcm_plugin.h
+++ b/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
   */
diff --git a/src/pcm/pcm_plug.c b/src/pcm/pcm_plug.c
index e5a3a189..287fb9f9 100644
--- a/src/pcm/pcm_plug.c
+++ b/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;
=========


Jaroslav, thanks a lot! I did not know it required just extending the nonlinear_preferred_formats, no further changes to the checks.

Tested on RPi4 HDMI, working fine. Please will you submit the patch, or should I prepare it based on your code?



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