Re: ASoC: amd: acp-pdm: full-scale burst on every DMIC capture start

From 56300d48776be7f8424ca96b5ca46b74383ba9d1 Mon Sep 17 00:00:00 2001
From: Vijendar Mukunda <[email protected]>
Date: Fri, 14 Aug 2026 12:42:27 +0530
Subject: [PATCH V2 0/3] ASoC: amd: ps: pdm: fix CIC decimator transients and resume BUG

The ACP PDM DMIC on Pink Sardine (ACP6.3/7.0/7.1) emits a full-scale
Nyquist-rate burst at the start of every capture stream and after a
system suspend/resume cycle.  This series fixes both cases and also
corrects a scheduling-while-atomic BUG introduced in v1 of the resume
fix.

Patch 1 adds a prepare() DAI callback that enables the PDM decimator
and waits 300 ms for the CIC filter chain to stabilise before the DMA
is armed. A new acp63_pause_pdm_dma() helper keeps the decimator
running across PAUSE_PUSH/PAUSE_RELEASE so no settling delay is needed
on pause resume.

Patch 2 extends the fix to the system resume path. After
TRIGGER_SUSPEND the decimator is disabled; because prepare() is not
called before TRIGGER_RESUME, the settle sequence must run elsewhere.
It is placed in acp63_pdm_resume() (SYSTEM_SLEEP_PM_OPS resume hook),
which runs in sleepable process context before the PCM layer issues
TRIGGER_RESUME. A shared acp63_pdm_settle() helper is factored out so
prepare() and acp63_pdm_resume() use identical logic.

Patch 3 marks the PDM DAI link nonatomic = 1 in the machine driver to
match the sleep requirements of the ops registered on the link.

Changes in v2:
  - Patch 1: no code changes.
  - Patch 2: fix scheduling-while-atomic BUG on s2idle resume reported
    by the reviewer.  v1 called acp63_pdm_settle() (msleep(300)) inside
    TRIGGER_RESUME, which runs under the PCM stream spinlock with IRQs
    disabled via snd_pcm_action_lock_irq().  This triggered:
      BUG: scheduling while atomic: .../0x00000002
      msleep
      acp63_pdm_dai_trigger+0x10d/0x2fc [snd_ps_pdm_dma]
      soc_dai_trigger.part.0 [snd_soc_core]
    Fix: move acp63_pdm_settle() from the trigger callback to
    acp63_pdm_resume(), which is sleepable.  Introduce the
    acp63_pdm_settle() helper so prepare() and acp63_pdm_resume() share
    the sequence without duplication.
  - Patch 3: new in v2. Marks the DAI link nonatomic = 1,
    to match the sleep requirements of the registered ops.

Vijendar Mukunda (3):
  ASoC: amd: ps: pdm: fix decimator transient on stream start
  ASoC: amd: ps: pdm: fix decimator transient on system resume
  ASoC: amd: ps: pdm: set PDM DAI link as non-atomic

 sound/soc/amd/ps/ps-mach.c    |   1 +
 sound/soc/amd/ps/ps-pdm-dma.c | 136 ++++++++++++++++++++++++++++++++--
 2 files changed, 131 insertions(+), 6 deletions(-)

-- 
2.48.1

From e0bc5065c65a6b7947a55ae4cd8d67826009f777 Mon Sep 17 00:00:00 2001
From: Vijendar Mukunda <[email protected]>
Date: Wed, 12 Aug 2026 14:41:42 +0530
Subject: [PATCH V2 1/3] ASoC: amd: ps: pdm: fix decimator transient on stream
 start

The ACP PDM DMIC emits a full-scale Nyquist-rate burst at the beginning
of every capture stream. The burst lasts ~4 ms on a warm start (ACP
already running) and ~250 ms on a cold start (ACP runtime-suspended),
and is audible to remote call participants as a click on join.

Root cause: acp63_start_pdm_dma() enables the PDM decimator and the DMA
in the same call, so the CIC filter chain's unflushed initial state goes
directly to userspace. An exponentially growing alternating pattern
collapses into full-scale saturation on both channels in antiphase --
the classic signature of a CIC integrator/comb chain running from a
non-zero initial condition.

Fix: add a prepare() DAI callback that enables PDM_ENABLE and waits
300 ms before the DMA starts. 300 ms is chosen to cover the cold-start
case; the warm-start transient clears in under 5 ms. After the
settling delay, flush ACP_WOV_PDM_FIFO_FLUSH so the DMA sees a clean
buffer.  acp63_start_pdm_dma() then only arms the DMA, skipping the
PDM_ENABLE write when prepare() has already set it.

For the RESUME path where prepare() is not called, PDM_ENABLE is set
conditionally in acp63_start_pdm_dma() if not already active.

PAUSE handling: PAUSE_PUSH previously disabled both the DMA and the PDM
decimator via acp63_stop_pdm_dma(). After moving PDM_ENABLE to
prepare(), ALSA does not call prepare() between PAUSE_PUSH and
PAUSE_RELEASE, so PAUSE_RELEASE would have re-enabled PDM without the
300 ms settling delay, reproducing the transient on every resume from
pause.

Fix the pause path by adding acp63_pause_pdm_dma(), which stops the DMA
only and leaves the PDM decimator running. PAUSE_RELEASE flushes the
FIFO to discard samples accumulated while the DMA was stopped, then
restarts the DMA.  Since the CIC filter never stopped, no settling delay
is needed. STOP and SUSPEND continue to use acp63_stop_pdm_dma(), which
disables both DMA and PDM.

Signed-off-by: Vijendar Mukunda <[email protected]>
---
 sound/soc/amd/ps/ps-pdm-dma.c | 103 ++++++++++++++++++++++++++++++++--
 1 file changed, 97 insertions(+), 6 deletions(-)

diff --git a/sound/soc/amd/ps/ps-pdm-dma.c b/sound/soc/amd/ps/ps-pdm-dma.c
index 04c014349347..e8f84d83a886 100644
--- a/sound/soc/amd/ps/ps-pdm-dma.c
+++ b/sound/soc/amd/ps/ps-pdm-dma.c
@@ -5,6 +5,7 @@
  * Copyright 2022, 2025 Advanced Micro Devices, Inc.
  */
 
+#include <linux/delay.h>
 #include <linux/platform_device.h>
 #include <linux/module.h>
 #include <linux/bitfield.h>
@@ -19,6 +20,17 @@
 
 #define DRV_NAME "acp_ps_pdm_dma"
 
+/*
+ * Time in milliseconds to wait after enabling the PDM clock before
+ * starting the DMA. The PDM microphone and the CIC/decimation filter
+ * chain need this time to reach a stable state; without it the first
+ * frames delivered to userspace contain a saturated Nyquist-rate
+ * transient (unflushed decimator initial state). 300 ms covers both
+ * the warm-start case (~4 ms) and the cold-start case (~250 ms, when
+ * the ACP has been runtime-suspended).
+ */
+#define PDM_SETTLING_DELAY_MS	300
+
 static int pdm_gain = 3;
 module_param(pdm_gain, int, 0644);
 MODULE_PARM_DESC(pdm_gain, "Gain control (0-3)");
@@ -107,12 +119,19 @@ static int acp63_start_pdm_dma(void __iomem *acp_base)
 	u32 pdm_dma_enable;
 	int timeout;
 
-	pdm_enable = 0x01;
-	pdm_dma_enable  = 0x01;
-
 	acp63_enable_pdm_clock(acp_base);
-	writel(pdm_enable, acp_base + ACP_WOV_PDM_ENABLE);
-	writel(pdm_dma_enable, acp_base + ACP_WOV_PDM_DMA_ENABLE);
+
+	/*
+	 * PDM_ENABLE and the clock were already set in prepare() for the
+	 * initial stream start to allow the CIC filter to settle. Only
+	 * write PDM_ENABLE if it is not already set, to cover the
+	 * RESUME and PAUSE_RELEASE paths where prepare() was not called.
+	 */
+	pdm_enable = readl(acp_base + ACP_WOV_PDM_ENABLE);
+	if (!(pdm_enable & ACP_PDM_ENABLE))
+		writel(ACP_PDM_ENABLE, acp_base + ACP_WOV_PDM_ENABLE);
+
+	writel(0x01, acp_base + ACP_WOV_PDM_DMA_ENABLE);
 	timeout = 0;
 	while (++timeout < ACP_COUNTER) {
 		pdm_dma_enable = readl(acp_base + ACP_WOV_PDM_DMA_ENABLE);
@@ -154,6 +173,32 @@ static int acp63_stop_pdm_dma(void __iomem *acp_base)
 	return 0;
 }
 
+static int acp63_pause_pdm_dma(void __iomem *acp_base)
+{
+	u32 pdm_dma_enable;
+	int timeout;
+
+	/*
+	 * Stop only the DMA; leave the PDM decimator running so that
+	 * PAUSE_RELEASE does not need to wait for the CIC filter to
+	 * settle again. The caller is responsible for flushing the FIFO
+	 * before restarting the DMA on PAUSE_RELEASE.
+	 */
+	pdm_dma_enable = readl(acp_base + ACP_WOV_PDM_DMA_ENABLE);
+	if (!(pdm_dma_enable & 0x01))
+		return 0;
+
+	writel(0x02, acp_base + ACP_WOV_PDM_DMA_ENABLE);
+	timeout = 0;
+	while (++timeout < ACP_COUNTER) {
+		pdm_dma_enable = readl(acp_base + ACP_WOV_PDM_DMA_ENABLE);
+		if ((pdm_dma_enable & 0x02) == 0x00)
+			return 0;
+		udelay(DELAY_US);
+	}
+	return -ETIMEDOUT;
+}
+
 static void acp63_config_dma(struct pdm_stream_instance *rtd, int direction)
 {
 	u16 page_idx;
@@ -286,6 +331,29 @@ static int acp63_pdm_dma_close(struct snd_soc_component *component,
 	return 0;
 }
 
+static int acp63_pdm_dma_prepare(struct snd_pcm_substream *substream,
+				  struct snd_soc_dai *dai)
+{
+	struct pdm_stream_instance *rtd = substream->runtime->private_data;
+
+	if (!rtd || substream->stream != SNDRV_PCM_STREAM_CAPTURE)
+		return 0;
+
+	/*
+	 * Enable the PDM decimator now, before the DMA starts. The
+	 * CIC filter chain and the microphone itself need time to reach
+	 * a stable state after the clock is applied. Without this
+	 * settling period the first frames captured by the DMA contain
+	 * a saturated Nyquist-rate transient. Wait for the decimator
+	 * to flush, then clear the FIFO so the DMA sees a clean buffer.
+	 */
+	acp63_enable_pdm_clock(rtd->acp63_base);
+	writel(ACP_PDM_ENABLE, rtd->acp63_base + ACP_WOV_PDM_ENABLE);
+	msleep(PDM_SETTLING_DELAY_MS);
+	writel(0x01, rtd->acp63_base + ACP_WOV_PDM_FIFO_FLUSH);
+	return 0;
+}
+
 static int acp63_pdm_dai_trigger(struct snd_pcm_substream *substream,
 				 int cmd, struct snd_soc_dai *dai)
 {
@@ -306,21 +374,43 @@ static int acp63_pdm_dai_trigger(struct snd_pcm_substream *substream,
 	switch (cmd) {
 	case SNDRV_PCM_TRIGGER_START:
 	case SNDRV_PCM_TRIGGER_RESUME:
+		writel(ch_mask, rtd->acp63_base + ACP_WOV_PDM_NO_OF_CHANNELS);
+		writel(PDM_DECIMATION_FACTOR, rtd->acp63_base + ACP_WOV_PDM_DECIMATION_FACTOR);
+		rtd->bytescount = acp63_pdm_get_byte_count(rtd, substream->stream);
+		pdm_status = acp63_check_pdm_dma_status(rtd->acp63_base);
+		if (!pdm_status)
+			ret = acp63_start_pdm_dma(rtd->acp63_base);
+		break;
 	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
 		writel(ch_mask, rtd->acp63_base + ACP_WOV_PDM_NO_OF_CHANNELS);
 		writel(PDM_DECIMATION_FACTOR, rtd->acp63_base + ACP_WOV_PDM_DECIMATION_FACTOR);
 		rtd->bytescount = acp63_pdm_get_byte_count(rtd, substream->stream);
+		/*
+		 * The PDM decimator was left running during PAUSE_PUSH so no
+		 * 300 ms settling delay is needed. Flush the FIFO to discard
+		 * samples accumulated while the DMA was stopped, then restart
+		 * the DMA.
+		 */
+		writel(0x01, rtd->acp63_base + ACP_WOV_PDM_FIFO_FLUSH);
 		pdm_status = acp63_check_pdm_dma_status(rtd->acp63_base);
 		if (!pdm_status)
 			ret = acp63_start_pdm_dma(rtd->acp63_base);
 		break;
 	case SNDRV_PCM_TRIGGER_STOP:
 	case SNDRV_PCM_TRIGGER_SUSPEND:
-	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
 		pdm_status = acp63_check_pdm_dma_status(rtd->acp63_base);
 		if (pdm_status)
 			ret = acp63_stop_pdm_dma(rtd->acp63_base);
 		break;
+	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
+		/*
+		 * Leave the PDM decimator running so that PAUSE_RELEASE does
+		 * not need the 300 ms CIC settling delay. Only stop the DMA.
+		 */
+		pdm_status = acp63_check_pdm_dma_status(rtd->acp63_base);
+		if (pdm_status)
+			ret = acp63_pause_pdm_dma(rtd->acp63_base);
+		break;
 	default:
 		ret = -EINVAL;
 		break;
@@ -329,6 +419,7 @@ static int acp63_pdm_dai_trigger(struct snd_pcm_substream *substream,
 }
 
 static const struct snd_soc_dai_ops acp63_pdm_dai_ops = {
+	.prepare   = acp63_pdm_dma_prepare,
 	.trigger   = acp63_pdm_dai_trigger,
 };
 
-- 
2.48.1

From 1f401ac36327baf67554612b01fd2831a1ac59eb Mon Sep 17 00:00:00 2001
From: Vijendar Mukunda <[email protected]>
Date: Fri, 14 Aug 2026 11:38:45 +0530
Subject: [PATCH V2 2/3] ASoC: amd: ps: pdm: fix decimator transient on system
 resume

After a system suspend/resume cycle with an active ALSA capture,
TRIGGER_RESUME fires after TRIGGER_SUSPEND without an intervening
prepare() call. TRIGGER_SUSPEND calls acp63_stop_pdm_dma() which
disables both the DMA and the PDM decimator. TRIGGER_RESUME then
called acp63_start_pdm_dma() which re-enables PDM and DMA together
without the 300 ms CIC settling delay or the FIFO flush, producing the
same Nyquist-rate transient that the prepare() fix was designed to
prevent. On hardware the transient caused an immediate XRUN and
broken-pipe error after wake.

Fix by adding the new acp63_pdm_settle() helper that encapsulates the
enable-clock / enable-PDM / msleep / flush-FIFO sequence, and calling
it from acp63_pdm_resume(), the system-sleep PM resume hook, which
runs in sleepable process context before the PCM layer issues
TRIGGER_RESUME. prepare() is also updated to call through this helper.

TRIGGER_RESUME runs under the PCM stream spinlock (IRQs disabled via
snd_pcm_action_lock_irq()), so msleep() is not permitted inside the
trigger callback. Placing the settle in acp63_pdm_resume() ensures the
CIC filter is stable before TRIGGER_RESUME fires, without sleeping in
atomic context.

Signed-off-by: Vijendar Mukunda <[email protected]>
---
 sound/soc/amd/ps/ps-pdm-dma.c | 41 +++++++++++++++++++++++++++++++----
 1 file changed, 37 insertions(+), 4 deletions(-)

diff --git a/sound/soc/amd/ps/ps-pdm-dma.c b/sound/soc/amd/ps/ps-pdm-dma.c
index e8f84d83a886..e48dfaf4908d 100644
--- a/sound/soc/amd/ps/ps-pdm-dma.c
+++ b/sound/soc/amd/ps/ps-pdm-dma.c
@@ -331,6 +331,20 @@ static int acp63_pdm_dma_close(struct snd_soc_component *component,
 	return 0;
 }
 
+/*
+ * acp63_pdm_settle - enable the PDM decimator and wait for it to stabilise.
+ *
+ * Called from prepare() and from TRIGGER_RESUME (where prepare() is not
+ * invoked by the ALSA core). Must not be called from atomic context.
+ */
+static void acp63_pdm_settle(void __iomem *acp_base)
+{
+	acp63_enable_pdm_clock(acp_base);
+	writel(ACP_PDM_ENABLE, acp_base + ACP_WOV_PDM_ENABLE);
+	msleep(PDM_SETTLING_DELAY_MS);
+	writel(0x01, acp_base + ACP_WOV_PDM_FIFO_FLUSH);
+}
+
 static int acp63_pdm_dma_prepare(struct snd_pcm_substream *substream,
 				  struct snd_soc_dai *dai)
 {
@@ -347,10 +361,7 @@ static int acp63_pdm_dma_prepare(struct snd_pcm_substream *substream,
 	 * a saturated Nyquist-rate transient. Wait for the decimator
 	 * to flush, then clear the FIFO so the DMA sees a clean buffer.
 	 */
-	acp63_enable_pdm_clock(rtd->acp63_base);
-	writel(ACP_PDM_ENABLE, rtd->acp63_base + ACP_WOV_PDM_ENABLE);
-	msleep(PDM_SETTLING_DELAY_MS);
-	writel(0x01, rtd->acp63_base + ACP_WOV_PDM_FIFO_FLUSH);
+	acp63_pdm_settle(rtd->acp63_base);
 	return 0;
 }
 
@@ -373,10 +384,24 @@ static int acp63_pdm_dai_trigger(struct snd_pcm_substream *substream,
 	}
 	switch (cmd) {
 	case SNDRV_PCM_TRIGGER_START:
+		writel(ch_mask, rtd->acp63_base + ACP_WOV_PDM_NO_OF_CHANNELS);
+		writel(PDM_DECIMATION_FACTOR, rtd->acp63_base + ACP_WOV_PDM_DECIMATION_FACTOR);
+		rtd->bytescount = acp63_pdm_get_byte_count(rtd, substream->stream);
+		pdm_status = acp63_check_pdm_dma_status(rtd->acp63_base);
+		if (!pdm_status)
+			ret = acp63_start_pdm_dma(rtd->acp63_base);
+		break;
 	case SNDRV_PCM_TRIGGER_RESUME:
 		writel(ch_mask, rtd->acp63_base + ACP_WOV_PDM_NO_OF_CHANNELS);
 		writel(PDM_DECIMATION_FACTOR, rtd->acp63_base + ACP_WOV_PDM_DECIMATION_FACTOR);
 		rtd->bytescount = acp63_pdm_get_byte_count(rtd, substream->stream);
+		/*
+		 * acp63_pdm_resume() already called acp63_pdm_settle() in
+		 * sleepable PM resume context before the PCM layer issued
+		 * TRIGGER_RESUME. The trigger callback runs under the PCM
+		 * stream spinlock (irqs disabled), so no msleep() is allowed
+		 * here. Just arm the DMA.
+		 */
 		pdm_status = acp63_check_pdm_dma_status(rtd->acp63_base);
 		if (!pdm_status)
 			ret = acp63_start_pdm_dma(rtd->acp63_base);
@@ -510,6 +535,14 @@ static int acp63_pdm_resume(struct device *dev)
 		acp63_config_dma(rtd, SNDRV_PCM_STREAM_CAPTURE);
 		acp63_init_pdm_ring_buffer(PDM_MEM_WINDOW_START, buffer_len,
 					   period_bytes, adata->acp63_base);
+		/*
+		 * TRIGGER_SUSPEND disabled the PDM decimator. The PCM layer
+		 * will issue TRIGGER_RESUME under the stream spinlock (IRQs
+		 * disabled), so msleep() is not permitted there. Run the
+		 * CIC settling sequence here in sleepable PM resume context
+		 * before the trigger fires.
+		 */
+		acp63_pdm_settle(rtd->acp63_base);
 	}
 	acp63_enable_pdm_interrupts(adata);
 	return 0;
-- 
2.48.1

From 56300d48776be7f8424ca96b5ca46b74383ba9d1 Mon Sep 17 00:00:00 2001
From: Vijendar Mukunda <[email protected]>
Date: Fri, 14 Aug 2026 11:39:10 +0530
Subject: [PATCH V2 3/3] ASoC: amd: ps: pdm: set PDM DAI link as non-atomic

The prepare() DAI callback calls msleep() via acp63_pdm_settle() to
allow the CIC filter to settle before DMA starts. Mark the DAI link
nonatomic = 1 so the trigger path is also nonatomic, matching the
sleep requirements of the ops registered on this link and preventing
any future msleep() inside the trigger from hitting a scheduling-while-
atomic BUG.

Signed-off-by: Vijendar Mukunda <[email protected]>
---
 sound/soc/amd/ps/ps-mach.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/sound/soc/amd/ps/ps-mach.c b/sound/soc/amd/ps/ps-mach.c
index 3e49c255c025..a040b5fcb0b7 100644
--- a/sound/soc/amd/ps/ps-mach.c
+++ b/sound/soc/amd/ps/ps-mach.c
@@ -32,6 +32,7 @@ static struct snd_soc_dai_link acp63_dai_pdm[] = {
 		.name = "acp63-dmic-capture",
 		.stream_name = "DMIC capture",
 		.capture_only = 1,
+		.nonatomic = 1,
 		SND_SOC_DAILINK_REG(acp63_pdm, dmic_codec, pdm_platform),
 	},
 };
-- 
2.48.1