[PATCH v3 4/5] soundwire: cadence: Fix lost ATTACHED interrupts when enumerating

[Richard Fitzgerald]

The correct way to handle interrupts is to clear the bits we
are about to handle _before_ handling them. Thus if the condition
then re-asserts during the handling we won't lose it.

This patch changes cdns_update_slave_status_work() to do this.

The previous code cleared the interrupts after handling them.
The problem with this is that when handling enumeration of devices
the ATTACH statuses can be accidentally cleared and so some or all
of the devices never complete their enumeration.

Thus we can have a situation like this:
- one or more devices are reverting to ID #0

- accumulated status bits indicate some devices attached and some
  on ID #0. (Remember: status bits are sticky until they are handled)

- Because of device on #0 sdw_handle_slave_status() programs the
  device ID and exits without handling the other status, expecting
  to get an ATTACHED from this reprogrammed device.

- The device immediately starts reporting ATTACHED in PINGs, which
  will assert its CDNS_MCP_SLAVE_INTSTAT_ATTACHED bit.

- cdns_update_slave_status_work() clears INTSTAT0/1. If the initial
  status had CDNS_MCP_SLAVE_INTSTAT_ATTACHED bit set it will be
  cleared.

- The ATTACHED change for the device has now been lost.

- cdns_update_slave_status_work() clears CDNS_MCP_INT_SLAVE_MASK so
  if the new ATTACHED state had set it, it will be cleared without
  ever having been handled.

Unless there is some other state change from another device to cause
a new interrupt, the ATTACHED state of the reprogrammed device will
never cause an interrupt so its enumeration will not be completed.

Signed-off-by: Richard Fitzgerald <rf@xxxxxxxxxxxxxxxxxxxxx>
---
 drivers/soundwire/cadence_master.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/drivers/soundwire/cadence_master.c b/drivers/soundwire/cadence_master.c
index 245191d22ccd..2f131604d884 100644
--- a/drivers/soundwire/cadence_master.c
+++ b/drivers/soundwire/cadence_master.c
@@ -954,9 +954,22 @@ static void cdns_update_slave_status_work(struct work_struct *work)
 	u32 device0_status;
 	int retry_count = 0;
 
+	/*
+	 * Clear main interrupt first so we don't lose any assertions
+	 * the happen during this function.
+	 */
+	cdns_writel(cdns, CDNS_MCP_INTSTAT, CDNS_MCP_INT_SLAVE_MASK);
+
 	slave0 = cdns_readl(cdns, CDNS_MCP_SLAVE_INTSTAT0);
 	slave1 = cdns_readl(cdns, CDNS_MCP_SLAVE_INTSTAT1);
 
+	/*
+	 * Clear the bits before handling so we don't lose any
+	 * bits that re-assert.
+	 */
+	cdns_writel(cdns, CDNS_MCP_SLAVE_INTSTAT0, slave0);
+	cdns_writel(cdns, CDNS_MCP_SLAVE_INTSTAT1, slave1);
+
 	/* combine the two status */
 	slave_intstat = ((u64)slave1 << 32) | slave0;
 
@@ -964,8 +977,6 @@ static void cdns_update_slave_status_work(struct work_struct *work)
 
 update_status:
 	cdns_update_slave_status(cdns, slave_intstat);
-	cdns_writel(cdns, CDNS_MCP_SLAVE_INTSTAT0, slave0);
-	cdns_writel(cdns, CDNS_MCP_SLAVE_INTSTAT1, slave1);
 
 	/*
 	 * When there is more than one peripheral per link, it's
@@ -982,6 +993,11 @@ static void cdns_update_slave_status_work(struct work_struct *work)
 	 * attention with PING commands. There is no need to check for
 	 * ALERTS since they are not allowed until a non-zero
 	 * device_number is assigned.
+	 *
+	 * Do not clear the INTSTAT0/1. While looping to enumerate devices on
+	 * #0 there could be status changes on other devices - these must
+	 * be kept in the INTSTAT so they can be handled when all #0 devices
+	 * have been handled.
 	 */
 
 	device0_status = cdns_readl(cdns, CDNS_MCP_SLAVE_STAT);
@@ -1001,8 +1017,7 @@ static void cdns_update_slave_status_work(struct work_struct *work)
 		}
 	}
 
-	/* clear and unmask Slave interrupt now */
-	cdns_writel(cdns, CDNS_MCP_INTSTAT, CDNS_MCP_INT_SLAVE_MASK);
+	/* unmask Slave interrupt now */
 	cdns_updatel(cdns, CDNS_MCP_INTMASK,
 		     CDNS_MCP_INT_SLAVE_MASK, CDNS_MCP_INT_SLAVE_MASK);
 
-- 
2.30.2