[PATCH] soundwire: cadence: fix race condition between suspend and Slave device alerts

[Bard Liao]

From: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>

In system suspend stress cases, the SOF CI reports timeouts. The root
cause is that an alert is generated while the system suspends. The
interrupt handling generates transactions on the bus that will never
be handled because the interrupts are disabled in parallel.

As a result, the transaction never completes and times out on resume.
This error doesn't seem too problematic since it happens in a work
queue, and the system recovers without issues.

Nevertheless, this race condition should not happen. When doing a
system suspend, or when disabling interrupts, we should make sure the
current transaction can complete, and prevent new work from being
queued.

BugLink: https://github.com/thesofproject/linux/issues/2344
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan at linux.intel.com>
Reviewed-by: Rander Wang <rander.wang at linux.intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao at linux.intel.com>
---
 drivers/soundwire/cadence_master.c | 24 +++++++++++++++++++++++-
 drivers/soundwire/cadence_master.h |  1 +
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/soundwire/cadence_master.c b/drivers/soundwire/cadence_master.c
index 24eafe0aa1c3..1330ffc47596 100644
--- a/drivers/soundwire/cadence_master.c
+++ b/drivers/soundwire/cadence_master.c
@@ -791,7 +791,16 @@ irqreturn_t sdw_cdns_irq(int irq, void *dev_id)
 			     CDNS_MCP_INT_SLAVE_MASK, 0);
 
 		int_status &= ~CDNS_MCP_INT_SLAVE_MASK;
-		schedule_work(&cdns->work);
+
+		/*
+		 * Deal with possible race condition between interrupt
+		 * handling and disabling interrupts on suspend.
+		 *
+		 * If the master is in the process of disabling
+		 * interrupts, don't schedule a workqueue
+		 */
+		if (cdns->interrupt_enabled)
+			schedule_work(&cdns->work);
 	}
 
 	cdns_writel(cdns, CDNS_MCP_INTSTAT, int_status);
@@ -924,6 +933,19 @@ int sdw_cdns_enable_interrupt(struct sdw_cdns *cdns, bool state)
 		slave_state = cdns_readl(cdns, CDNS_MCP_SLAVE_INTSTAT1);
 		cdns_writel(cdns, CDNS_MCP_SLAVE_INTSTAT1, slave_state);
 	}
+	cdns->interrupt_enabled = state;
+
+	/*
+	 * Complete any on-going status updates before updating masks,
+	 * and cancel queued status updates.
+	 *
+	 * There could be a race with a new interrupt thrown before
+	 * the 3 mask updates below are complete, so in the interrupt
+	 * we use the 'interrupt_enabled' status to prevent new work
+	 * from being queued.
+	 */
+	if (!state)
+		cancel_work_sync(&cdns->work);
 
 	cdns_writel(cdns, CDNS_MCP_SLAVE_INTMASK0, slave_intmask0);
 	cdns_writel(cdns, CDNS_MCP_SLAVE_INTMASK1, slave_intmask1);
diff --git a/drivers/soundwire/cadence_master.h b/drivers/soundwire/cadence_master.h
index fdec62b912d3..4d1aab5b5ec2 100644
--- a/drivers/soundwire/cadence_master.h
+++ b/drivers/soundwire/cadence_master.h
@@ -133,6 +133,7 @@ struct sdw_cdns {
 
 	bool link_up;
 	unsigned int msg_count;
+	bool interrupt_enabled;
 
 	struct work_struct work;
 
-- 
2.17.1