From 8bf0e04c1629dcecf68035bb94a036b29b918005 Mon Sep 17 00:00:00 2001
From: Jelle Raaijmakers <jelle@gmta.nl>
Date: Sat, 26 Feb 2022 19:20:07 +0100
Subject: [PATCH] Kernel: Allow setting AC'97 sample rate during playback

The Qemu AC'97 device stops its PCM channel's DMA engine when it is
running and the sample rate is changed. We now make sure the DMA engine
is restarted after changing the sample rate, allowing you to e.g. run
`asctl set r 22050` during `aplay` playback.
---
 Kernel/Devices/Audio/AC97.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Kernel/Devices/Audio/AC97.cpp b/Kernel/Devices/Audio/AC97.cpp
index 09dca53a56..68f7c51420 100644
--- a/Kernel/Devices/Audio/AC97.cpp
+++ b/Kernel/Devices/Audio/AC97.cpp
@@ -145,6 +145,10 @@ ErrorOr<void> AC97::set_pcm_output_sample_rate(u32 sample_rate)
 
     dbgln("AC97 @ {}: PCM front DAC rate set to {} Hz", pci_address(), m_sample_rate);
 
+    // Setting the sample rate stops a running DMA engine, so restart it
+    if (m_pcm_out_channel.dma_running())
+        m_pcm_out_channel.start_dma();
+
     return {};
 }