From 77cf7bdb28dd62199356bbcf3558f6c2281c80cf Mon Sep 17 00:00:00 2001
From: Andrea Bondavalli <andrea.bondavalli74@gmail.com>
Date: Wed, 3 Feb 2021 18:41:00 +0100
Subject: [PATCH] Added patch to Ravenna driver to fix a problem that leads to
 an initial playback buffer corruption in case the read/write interleaved mode
 is used. The problem arises from pre-buffering performed after ALSA prepare
 and before ALSA start trigger- The patch enables the early startup of the
 audio playback interrupt and disables the cleanup (mute) of the playback
 buffer. This issue can be reproduced using the test suite developed to
 investigate #17 and by removing the (-M) option from aplay in run_test.sh
 script.

---
 .../ravenna-alsa-fix-playback-rw-mode.patch   | 26 +++++++++++++++++++
 build.sh                                      |  1 +
 2 files changed, 27 insertions(+)
 create mode 100644 3rdparty/patches/ravenna-alsa-fix-playback-rw-mode.patch

diff --git a/3rdparty/patches/ravenna-alsa-fix-playback-rw-mode.patch b/3rdparty/patches/ravenna-alsa-fix-playback-rw-mode.patch
new file mode 100644
index 0000000..5961fbd
--- /dev/null
+++ b/3rdparty/patches/ravenna-alsa-fix-playback-rw-mode.patch
@@ -0,0 +1,26 @@
+diff --git a/driver/audio_driver.c b/driver/audio_driver.c
+index 3d9debd..cc6240e 100644
+--- a/driver/audio_driver.c
++++ b/driver/audio_driver.c
+@@ -936,6 +936,8 @@
+             chip->dma_playback_offset = 0;
+             chip->dma_playback_buffer = runtime->dma_area;
+             chip->pcm_playback_buffer_size = snd_pcm_lib_buffer_bytes(chip->playback_substream);
++            // early startup to fix problem with read-write interleaved mode pre-buffering
++            chip->mr_alsa_audio_ops->start_interrupts(chip->ravenna_peer, 1);
+         }
+         else if(substream->stream == SNDRV_PCM_STREAM_CAPTURE)
+         {
+index 5a90eca..8023708 100644
+--- a/driver/manager.c
++++ b/driver/manager.c
+@@ -279,7 +279,7 @@
+     }
+     else {
+         printk(KERN_DEBUG "starting playback I/O\n");
+-        MuteOutputBuffer(self);
++        //MuteOutputBuffer(self);
+         self->m_bIsPlaybackIO = true;
+     }
+
+
diff --git a/build.sh b/build.sh
index d68eeec..be3554a 100755
--- a/build.sh
+++ b/build.sh
@@ -25,6 +25,7 @@ if [ ! -d ravenna-alsa-lkm.git ]; then
   git apply ../patches/ravenna-alsa-lkm-direct-pcm-transfer.patch
   git apply ../patches/ravenna-alsa-lkm-enable-mono-channels.patch
   git apply ../patches/ravenna-alsa-lkm-init-play-capture-buffers.patch
+  git apply ../patches/ravenna-alsa-fix-playback-rw-mode.patch
   echo "Building ravenna-alsa-lkm kernel module ..."
   cd driver
   make