alsa: Try to use sysdefault if default device has not been set

In some configurations there is no "default" device at all, but there
may be "sysdefault" device. Outputting to non-existent "default" device
in some systems seems to cause buffer underrun errors to occur.

Task-number: QTBUG-114900
Pick-to: 6.6 6.5
Change-Id: I5311ec95af8938aa04ddec838b762ab3482f953f
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
(cherry picked from commit e54f02fde0cb2902e367468107709d17a3a1a60c)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 11 insertions, 1 deletions

diff --git a/src/multimedia/alsa/qalsamediadevices.cpp b/src/multimedia/alsa/qalsamediadevices.cpp
index 98b4c1362..5a133e9d1 100644
--- a/src/multimedia/alsa/qalsamediadevices.cpp
+++ b/src/multimedia/alsa/qalsamediadevices.cpp
@@ -41,6 +41,8 @@ static QList<QAudioDevice> availableDevices(QAudioDevice::Mode mode)
         filter = "Output";
     }
 
+    QAlsaAudioDeviceInfo* sysdefault = nullptr;
+
     while (*n != NULL) {
         name = snd_device_name_get_hint(*n, "NAME");
         if (name != 0 && qstrcmp(name, "null") != 0) {
@@ -50,10 +52,13 @@ static QList<QAudioDevice> availableDevices(QAudioDevice::Mode mode)
             if ((descr != NULL) && ((io == NULL) || (io == filter))) {
                 auto *infop = new QAlsaAudioDeviceInfo(name, QString::fromUtf8(descr), mode);
                 devices.append(infop->create());
-                if (strcmp(name, "default") == 0) {
+                if (!hasDefault && strcmp(name, "default") == 0) {
                     infop->isDefault = true;
                     hasDefault = true;
                 }
+                else if (!sysdefault && !hasDefault && strcmp(name, "sysdefault") == 0) {
+                    sysdefault = infop;
+                }
             }
 
             free(descr);
@@ -64,6 +69,11 @@ static QList<QAudioDevice> availableDevices(QAudioDevice::Mode mode)
     }
     snd_device_name_free_hint(hints);
 
+    if (!hasDefault && sysdefault) {
+        // Make "sysdefault" the default device if there is no "default" device exists
+        sysdefault->isDefault = true;
+        hasDefault = true;
+    }
     if (!hasDefault && devices.size() > 0) {
         auto infop = new QAlsaAudioDeviceInfo("default", QString(), QAudioDevice::Output);
         infop->isDefault = true;