kselftest: alsa: Use private alsa-lib configuration in mixer test

As mentined by Takashi Sakamoto, the system-wide alsa-lib configuration
may override the standard device declarations. This patch use the private
alsa-lib configuration to set the predictable environment.
Signed-off-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20211208095209.1772296-1-perex@perex.cz
[Restructure version test to keep the preprocessor happy -- broonie]
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20211210185410.740009-4-broonie@kernel.orgSigned-off-by: Takashi Iwai <tiwai@suse.de>

tools/testing/selftests/alsa/mixer-test.c

@@ -46,22 +46,74 @@ struct ctl_data {
 	struct ctl_data *next;
 };
 
+static const char *alsa_config =
+"ctl.hw {\n"
+"	@args [ CARD ]\n"
+"	@args.CARD.type string\n"
+"	type hw\n"
+"	card $CARD\n"
+"}\n"
+;
+
 int num_cards = 0;
 int num_controls = 0;
 struct card_data *card_list = NULL;
 struct ctl_data *ctl_list = NULL;
 
+#ifdef SND_LIB_VER
+#if SND_LIB_VERSION >= SND_LIB_VER(1, 2, 6)
+#define LIB_HAS_LOAD_STRING
+#endif
+#endif
+
+#ifndef LIB_HAS_LOAD_STRING
+int snd_config_load_string(snd_config_t **config, const char *s, size_t size)
+{
+	snd_input_t *input;
+	snd_config_t *dst;
+	int err;
+
+	assert(config && s);
+	if (size == 0)
+		size = strlen(s);
+	err = snd_input_buffer_open(&input, s, size);
+	if (err < 0)
+		return err;
+	err = snd_config_top(&dst);
+	if (err < 0) {
+		snd_input_close(input);
+		return err;
+	}
+	err = snd_config_load(dst, input);
+	snd_input_close(input);
+	if (err < 0) {
+		snd_config_delete(dst);
+		return err;
+	}
+	*config = dst;
+	return 0;
+}
+#endif
+
 void find_controls(void)
 {
 	char name[32];
 	int card, ctl, err;
 	struct card_data *card_data;
 	struct ctl_data *ctl_data;
+	snd_config_t *config;
 
 	card = -1;
 	if (snd_card_next(&card) < 0 || card < 0)
 		return;
 
+	err = snd_config_load_string(&config, alsa_config, strlen(alsa_config));
+	if (err < 0) {
+		ksft_print_msg("Unable to parse custom alsa-lib configuration: %s\n",
+			       snd_strerror(err));
+		ksft_exit_fail();
+	}
+
 	while (card >= 0) {
 		sprintf(name, "hw:%d", card);
 
@@ -69,7 +121,7 @@ void find_controls(void)
 		if (!card_data)
 			ksft_exit_fail_msg("Out of memory\n");
 
-		err = snd_ctl_open(&card_data->handle, name, 0);
+		err = snd_ctl_open_lconf(&card_data->handle, name, 0, config);
 		if (err < 0) {
 			ksft_print_msg("Failed to get hctl for card %d: %s\n",
 				       card, snd_strerror(err));
@@ -137,6 +189,8 @@ void find_controls(void)
 			break;
 		}
 	}
+
+	snd_config_delete(config);
 }
 
 /*