[PATCH] soundwire: intel_bus_common: enable interrupts before exiting reset

[Bard Liao <yung-chuan.liao@xxxxxxxxxxxxxxx>]

From: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>

The existing code enables the Cadence IP interrupts after the bus
reset sequence. The problem with this sequence is that it might be
pre-empted, giving SoundWire devices time to sync and report as
ATTACHED before the interrupts are enabled. In that case, the Cadence
IP will not detect a state change and will not throw an interrupt to
proceed with the enumeration of a Device0.

In our overnight stress tests, we observed that a slight
sub-millisecond delay in enabling interrupts after the reset was
correlated with detection failures. This problem is more prevalent on
the LunarLake silicon, likely due to SOC integration changes, but it
was observed on earlier generations as well.

This patch reverts the sequence, with the interrupts enabled before
performing the bus reset. This removes the race condition and makes
sure the Cadence IP is able to detect the presence of a Device0 in all
cases.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
Signed-off-by: Bard Liao <yung-chuan.liao@xxxxxxxxxxxxxxx>
---
 drivers/soundwire/intel_bus_common.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/drivers/soundwire/intel_bus_common.c b/drivers/soundwire/intel_bus_common.c
index 2bc960d05780..d3ff6c65b64c 100644
--- a/drivers/soundwire/intel_bus_common.c
+++ b/drivers/soundwire/intel_bus_common.c
@@ -45,18 +45,18 @@ int intel_start_bus(struct sdw_intel *sdw)
 		return ret;
 	}
 
+	ret = sdw_cdns_enable_interrupt(cdns, true);
+	if (ret < 0) {
+		dev_err(dev, "%s: cannot enable interrupts: %d\n", __func__, ret);
+		return ret;
+	}
+
 	ret = sdw_cdns_exit_reset(cdns);
 	if (ret < 0) {
 		dev_err(dev, "%s: unable to exit bus reset sequence: %d\n", __func__, ret);
 		return ret;
 	}
 
-	ret = sdw_cdns_enable_interrupt(cdns, true);
-	if (ret < 0) {
-		dev_err(dev, "%s: cannot enable interrupts: %d\n", __func__, ret);
-		return ret;
-	}
-
 	sdw_cdns_check_self_clearing_bits(cdns, __func__,
 					  true, INTEL_MASTER_RESET_ITERATIONS);
 
@@ -139,18 +139,18 @@ int intel_start_bus_after_reset(struct sdw_intel *sdw)
 			return ret;
 		}
 
+		ret = sdw_cdns_enable_interrupt(cdns, true);
+		if (ret < 0) {
+			dev_err(dev, "cannot enable interrupts during resume\n");
+			return ret;
+		}
+
 		ret = sdw_cdns_exit_reset(cdns);
 		if (ret < 0) {
 			dev_err(dev, "unable to exit bus reset sequence during resume\n");
 			return ret;
 		}
 
-		ret = sdw_cdns_enable_interrupt(cdns, true);
-		if (ret < 0) {
-			dev_err(dev, "cannot enable interrupts during resume\n");
-			return ret;
-		}
-
 	}
 	sdw_cdns_check_self_clearing_bits(cdns, __func__, true, INTEL_MASTER_RESET_ITERATIONS);
 
-- 
2.43.0