soundwire: intel: don't save hw_params for use in prepare

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>
Link: https://lore.kernel.org/r/20230321022642.1426611-1-yung-chuan.liao@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

1 files changed, 0 insertions, 2 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;