remove pcm_prepare in pcm_open

For the dynamic pcm device, it is valid to specify the backend after
opening it. However, it is invalid to call prepare on a dynamic pcm
device without connecting any backend device. We should not do
pcm_prepare in pcm_open.

See also: Issue #197

examples/pcm-readi.c

@@ -29,6 +29,7 @@ static size_t read_frames(void **frames)
         fprintf(stderr, "failed to open PCM\n");
         return 0;
     }
+    pcm_prepare(pcm);
 
     unsigned int frame_size = pcm_frames_to_bytes(pcm, 1);
     unsigned int frames_per_sec = pcm_get_rate(pcm);

examples/pcm-writei.c

@@ -70,6 +70,7 @@ static int write_frames(const void * frames, size_t byte_count){
         fprintf(stderr, "failed to open PCM\n");
         return -1;
     }
+    pcm_prepare(pcm);
 
     unsigned int frame_count = pcm_bytes_to_frames(pcm, byte_count);
 

src/pcm.c

@@ -1101,10 +1101,6 @@ struct pcm *pcm_open(unsigned int card, unsigned int device,
     }
 #endif
 
-    /* prepare here so the user does not need to do this later */
-    if (pcm_prepare(pcm))
-        goto fail;
-
     pcm->xruns = 0;
     return pcm;
 

tests/src/pcm_in_test.cc

@@ -47,6 +47,7 @@ class PcmInTest : public ::testing::Test {
         pcm_object = pcm_open(kLoopbackCard, kLoopbackCaptureDevice, PCM_IN, &kDefaultConfig);
         ASSERT_NE(pcm_object, nullptr);
         ASSERT_TRUE(pcm_is_ready(pcm_object));
+        pcm_prepare(pcm_object);
     }
 
     virtual void TearDown() override {

tests/src/pcm_loopback_test.cc

@@ -160,6 +160,7 @@ TEST(PcmLoopbackTest, LoopbackS16le) {
     };
     pcm *pcm_in = pcm_open(kLoopbackCard, kLoopbackCaptureDevice, PCM_IN, &kInConfig);
     ASSERT_TRUE(pcm_is_ready(pcm_in));
+    pcm_prepare(pcm_in);
 
     static constexpr pcm_config kOutConfig = {
         .channels = kDefaultChannels,
@@ -174,6 +175,7 @@ TEST(PcmLoopbackTest, LoopbackS16le) {
     };
     pcm *pcm_out = pcm_open(kLoopbackCard, kLoopbackPlaybackDevice, PCM_OUT, &kOutConfig);
     ASSERT_TRUE(pcm_is_ready(pcm_out));
+    pcm_prepare(pcm_out);
 
     ASSERT_EQ(pcm_link(pcm_in, pcm_out), 0);
 

tests/src/pcm_out_test.cc

@@ -47,6 +47,7 @@ class PcmOutTest : public ::testing::Test {
         pcm_object = pcm_open(kLoopbackCard, kLoopbackPlaybackDevice, PCM_OUT, &kDefaultConfig);
         ASSERT_NE(pcm_object, nullptr);
         ASSERT_TRUE(pcm_is_ready(pcm_object));
+        pcm_prepare(pcm_object);
     }
 
     virtual void TearDown() override {
@@ -176,6 +177,7 @@ class PcmOutMmapTest : public PcmOutTest {
                 &kDefaultConfig);
         ASSERT_NE(pcm_object, nullptr);
         ASSERT_TRUE(pcm_is_ready(pcm_object));
+        pcm_prepare(pcm_object);
     }
 
     virtual void TearDown() override {

utils/tinycap.c

@@ -231,6 +231,7 @@ unsigned int capture_sample(FILE *file, unsigned int card, unsigned int device,
                 pcm_get_error(pcm));
         return 0;
     }
+    pcm_prepare(pcm);
 
     size = pcm_frames_to_bytes(pcm, pcm_get_buffer_size(pcm));
     buffer = malloc(size);

utils/tinyplay.c

@@ -192,6 +192,7 @@ int ctx_init(struct ctx* ctx, const struct cmd *cmd)
         pcm_close(ctx->pcm);
         return -1;
     }
+    pcm_prepare(ctx->pcm);
 
     return 0;
 }