From:   Bard Liao <yung-chuan.liao@linux.intel.com>
To:     alsa-devel@alsa-project.org, vkoul@kernel.org
Cc:     vinod.koul@linaro.org, linux-kernel@vger.kernel.org,
        pierre-louis.bossart@linux.intel.com, bard.liao@intel.com
Subject: [PATCH] soundwire: intel: don't save hw_params for use in prepare
Date:   Tue, 21 Mar 2023 10:26:42 +0800
Message-Id: <20230321022642.1426611-1-yung-chuan.liao@linux.intel.com>
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From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>

The existing code copies the hw_params pointer and reuses it later in
.prepare, specifically to re-initialize the ALH DMA channel
information that's lost in suspend-resume cycles.

This is not needed, we can directly access the information from the
substream/rtd - as done for the HDAudio DAIs in
sound/soc/sof/intel/hda-dai.c

In addition, using the saved pointer causes the suspend-resume test
cases to fail on specific platforms, depending on which version of GCC
is used. Péter Ujfalusi and I have spent long hours to root-cause this
problem that was reported by the Intel CI first with 6.2-rc1 and again
v6.3-rc1. In the latter case we were lucky that the problem was 100%
reproducible on local test devices, and found out that adding a
dev_dbg() or adding a call to usleep_range() just before accessing the
saved pointer "fixed" the issue. With errors appearing just by
changing the compiler version or minor changes in the code generated,
clearly we have a memory management Heisenbug.

The root-cause seems to be that the hw_params pointer is not
persistent. The soc-pcm code allocates the hw_params structure on the
stack, and passes it to the BE dailink hw_params and DAIs
hw_params. Saving such a pointer and reusing it later during the
.prepare stage cannot possibly work reliably, it's broken-by-design
since v5.10. It's astonishing that the problem was not seen earlier.

This simple fix will have to be back-ported to -stable, due to changes
to avoid the use of the get/set_dmadata routines this patch will only
apply on kernels older than v6.1.

Fixes: a5a0239c27fe ("soundwire: intel: reinitialize IP+DSP in .prepare(), but only when resuming")
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Reviewed-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
---
 drivers/soundwire/cadence_master.h |  2 --
 drivers/soundwire/intel.c          | 11 +++++++----
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/soundwire/cadence_master.h b/drivers/soundwire/cadence_master.h
index b653734085d9..27c56274217f 100644
--- a/drivers/soundwire/cadence_master.h
+++ b/drivers/soundwire/cadence_master.h
@@ -84,7 +84,6 @@ struct sdw_cdns_stream_config {
  * @bus: Bus handle
  * @stream_type: Stream type
  * @link_id: Master link id
- * @hw_params: hw_params to be applied in .prepare step
  * @suspended: status set when suspended, to be used in .prepare
  * @paused: status set in .trigger, to be used in suspend
  * @direction: stream direction
@@ -96,7 +95,6 @@ struct sdw_cdns_dai_runtime {
 	struct sdw_bus *bus;
 	enum sdw_stream_type stream_type;
 	int link_id;
-	struct snd_pcm_hw_params *hw_params;
 	bool suspended;
 	bool paused;
 	int direction;
diff --git a/drivers/soundwire/intel.c b/drivers/soundwire/intel.c
index 046c67a2a39b..238acf5c97a9 100644
--- a/drivers/soundwire/intel.c
+++ b/drivers/soundwire/intel.c
@@ -725,7 +725,6 @@ static int intel_hw_params(struct snd_pcm_substream *substream,
 	dai_runtime->paused = false;
 	dai_runtime->suspended = false;
 	dai_runtime->pdi = pdi;
-	dai_runtime->hw_params = params;
 
 	/* Inform DSP about PDI stream number */
 	ret = intel_params_stream(sdw, substream->stream, dai, params,
@@ -778,6 +777,11 @@ static int intel_prepare(struct snd_pcm_substream *substream,
 	}
 
 	if (dai_runtime->suspended) {
+		struct snd_soc_pcm_runtime *rtd = asoc_substream_to_rtd(substream);
+		struct snd_pcm_hw_params *hw_params;
+
+		hw_params = &rtd->dpcm[substream->stream].hw_params;
+
 		dai_runtime->suspended = false;
 
 		/*
@@ -789,7 +793,7 @@ static int intel_prepare(struct snd_pcm_substream *substream,
 		 */
 
 		/* configure stream */
-		ch = params_channels(dai_runtime->hw_params);
+		ch = params_channels(hw_params);
 		if (substream->stream == SNDRV_PCM_STREAM_CAPTURE)
 			dir = SDW_DATA_DIR_RX;
 		else
@@ -801,7 +805,7 @@ static int intel_prepare(struct snd_pcm_substream *substream,
 
 		/* Inform DSP about PDI stream number */
 		ret = intel_params_stream(sdw, substream->stream, dai,
-					  dai_runtime->hw_params,
+					  hw_params,
 					  sdw->instance,
 					  dai_runtime->pdi->intel_alh_id);
 	}
@@ -840,7 +844,6 @@ intel_hw_free(struct snd_pcm_substream *substream, struct snd_soc_dai *dai)
 		return ret;
 	}
 
-	dai_runtime->hw_params = NULL;
 	dai_runtime->pdi = NULL;
 
 	return 0;
-- 
2.25.1