[PATCH 6/6] soundwire: qcom: do not probe devices before bus/link init

[Krzysztof Kozlowski]

Soundwire devices are supposed to be kept in reset state (powered off)
till their probe() or component bind() callbacks.  However if they are
already powered on, then they might enumerate before the master
initializes bus in qcom_swrm_init() leading to occasional errors like:

  qcom-soundwire 6d30000.soundwire-controller: Qualcomm Soundwire controller v2.0.0 Registered
  wcd938x_codec audio-codec: bound sdw:0:0217:010d:00:4 (ops wcd938x_sdw_component_ops)
  wcd938x_codec audio-codec: bound sdw:0:0217:010d:00:3 (ops wcd938x_sdw_component_ops)
  qcom-soundwire 6ad0000.soundwire-controller: swrm_wait_for_wr_fifo_avail err write overflow

The problem primarily lies in Qualcomm Soundwire controller probe() sequence:
1. request_threaded_irq()
2. sdw_bus_master_add() - which will cause probe() and component bind()
   of Soundwire devices, e.g. WCD938x codec drivers.  Device drivers
   might already start accessing their registers.
3. qcom_swrm_init() - which initializes the link/bus and enables
   interrupts.

Any access to device registers at (2) above, will fail because link/bus
is not yet initialized.

However the fix is not as simple as moving qcom_swrm_init() before
sdw_bus_master_add(), because this will cause early interrupt of new
slave attached.  The interrupt handler expects bus master (ctrl->bus.md)
to be allocated, so this would lead to NULL pointer exception.

Rework the init sequence and change the interrupt handler.  The correct
sequence fixing accessing device registers before link init is now:
1. qcom_swrm_init()
2. request_threaded_irq()
3. sdw_bus_master_add()
which still might cause early interrupts, if Soundwire devices are not
in powered off state before their probe.  This early interrupt issue is
fixed by checking if bus master (ctrl->bus.md) was allocated and if not,
scheduling delayed work for enumerating the slave device.  Since we
actually can handle early interrupt now, drop IRQF_TRIGGER_RISING flag
from the interrupt, because it is not really valid and driver should use
flags provided by DTS.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>

---

Change context depends on:
https://lore.kernel.org/r/20230209131336.18252-3-srinivas.kandagatla@xxxxxxxxxx
https://lore.kernel.org/all/20230418095447.577001-1-krzysztof.kozlowski@xxxxxxxxxx/

Cc: Patrick Lai <quic_plai@xxxxxxxxxxx>
---
 drivers/soundwire/qcom.c | 89 ++++++++++++++++++++++++++++++++--------
 1 file changed, 72 insertions(+), 17 deletions(-)

diff --git a/drivers/soundwire/qcom.c b/drivers/soundwire/qcom.c
index 679990dc3cc4..802d939ce7aa 100644
--- a/drivers/soundwire/qcom.c
+++ b/drivers/soundwire/qcom.c
@@ -19,6 +19,7 @@
 #include <linux/slimbus.h>
 #include <linux/soundwire/sdw.h>
 #include <linux/soundwire/sdw_registers.h>
+#include <linux/workqueue.h>
 #include <sound/pcm_params.h>
 #include <sound/soc.h>
 #include "bus.h"
@@ -187,6 +188,7 @@ struct qcom_swrm_ctrl {
 #endif
 	struct completion broadcast;
 	struct completion enumeration;
+	struct delayed_work new_slave_work;
 	/* Port alloc/free lock */
 	struct mutex port_lock;
 	struct clk *hclk;
@@ -606,6 +608,37 @@ static int qcom_swrm_enumerate(struct sdw_bus *bus)
 	return 0;
 }
 
+static void qcom_swrm_new_slave(struct work_struct *work)
+{
+	struct qcom_swrm_ctrl *ctrl = container_of(work, struct qcom_swrm_ctrl,
+						   new_slave_work.work);
+
+	/*
+	 * All Soundwire slave deviecs are expected to be in reset state (powered down)
+	 * during sdw_bus_master_add().  The slave device should be brougth
+	 * from reset by its probe() or bind() function, as a result of
+	 * sdw_bus_master_add().
+	 * Add a simple check to avoid NULL pointer except on early interrupts.
+	 * Note that if this condition happens, the slave device will not be
+	 * enumerated. Its driver should be fixed.
+	 *
+	 * smp_load_acquire() paired with sdw_master_device_add().
+	 */
+	if (!smp_load_acquire(&ctrl->bus.md)) {
+		dev_err(ctrl->dev,
+			"Got unexpected, early interrupt, device will not be enumerated\n");
+		return;
+	}
+
+	clk_prepare_enable(ctrl->hclk);
+
+	qcom_swrm_get_device_status(ctrl);
+	qcom_swrm_enumerate(&ctrl->bus);
+	sdw_handle_slave_status(&ctrl->bus, ctrl->status);
+
+	clk_disable_unprepare(ctrl->hclk);
+};
+
 static irqreturn_t qcom_swrm_wake_irq_handler(int irq, void *dev_id)
 {
 	struct qcom_swrm_ctrl *ctrl = dev_id;
@@ -668,9 +701,17 @@ static irqreturn_t qcom_swrm_irq_handler(int irq, void *dev_id)
 					dev_dbg(ctrl->dev, "Slave status not changed %x\n",
 						slave_status);
 				} else {
-					qcom_swrm_get_device_status(ctrl);
-					qcom_swrm_enumerate(&ctrl->bus);
-					sdw_handle_slave_status(&ctrl->bus, ctrl->status);
+					unsigned long delay = 0;
+
+					/*
+					 * See qcom_swrm_new_slave() for
+					 * explanation. smp_load_acquire() paired
+					 * with sdw_master_device_add().
+					 */
+					if (!smp_load_acquire(&ctrl->bus.md))
+						delay = 10;
+					schedule_delayed_work(&ctrl->new_slave_work,
+							      delay);
 				}
 				break;
 			case SWRM_INTERRUPT_STATUS_MASTER_CLASH_DET:
@@ -780,6 +821,7 @@ static int qcom_swrm_init(struct qcom_swrm_ctrl *ctrl)
 
 	ctrl->intr_mask = SWRM_INTERRUPT_STATUS_RMSK;
 	/* Mask soundwire interrupts */
+
 	if (ctrl->version < SWRM_VERSION_2_0_0)
 		ctrl->reg_write(ctrl, ctrl->reg_layout[SWRM_REG_INTERRUPT_MASK_ADDR],
 				SWRM_INTERRUPT_STATUS_RMSK);
@@ -1485,6 +1527,7 @@ static int qcom_swrm_probe(struct platform_device *pdev)
 	mutex_init(&ctrl->port_lock);
 	init_completion(&ctrl->broadcast);
 	init_completion(&ctrl->enumeration);
+	INIT_DELAYED_WORK(&ctrl->new_slave_work, qcom_swrm_new_slave);
 
 	ctrl->bus.ops = &qcom_swrm_ops;
 	ctrl->bus.port_ops = &qcom_swrm_port_ops;
@@ -1514,9 +1557,10 @@ static int qcom_swrm_probe(struct platform_device *pdev)
 
 	ctrl->reg_read(ctrl, SWRM_COMP_HW_VERSION, &ctrl->version);
 
+	qcom_swrm_init(ctrl);
+
 	ret = devm_request_threaded_irq(dev, ctrl->irq, NULL,
 					qcom_swrm_irq_handler,
-					IRQF_TRIGGER_RISING |
 					IRQF_ONESHOT,
 					"soundwire", ctrl);
 	if (ret) {
@@ -1524,18 +1568,6 @@ static int qcom_swrm_probe(struct platform_device *pdev)
 		goto err_clk;
 	}
 
-	ctrl->wake_irq = of_irq_get(dev->of_node, 1);
-	if (ctrl->wake_irq > 0) {
-		ret = devm_request_threaded_irq(dev, ctrl->wake_irq, NULL,
-						qcom_swrm_wake_irq_handler,
-						IRQF_TRIGGER_HIGH | IRQF_ONESHOT,
-						"swr_wake_irq", ctrl);
-		if (ret) {
-			dev_err(dev, "Failed to request soundwire wake irq\n");
-			goto err_init;
-		}
-	}
-
 	pm_runtime_set_autosuspend_delay(dev, 3000);
 	pm_runtime_use_autosuspend(dev);
 	pm_runtime_mark_last_busy(dev);
@@ -1549,7 +1581,18 @@ static int qcom_swrm_probe(struct platform_device *pdev)
 		goto err_clk;
 	}
 
-	qcom_swrm_init(ctrl);
+	ctrl->wake_irq = of_irq_get(dev->of_node, 1);
+	if (ctrl->wake_irq > 0) {
+		ret = devm_request_threaded_irq(dev, ctrl->wake_irq, NULL,
+						qcom_swrm_wake_irq_handler,
+						IRQF_TRIGGER_HIGH | IRQF_ONESHOT,
+						"swr_wake_irq", ctrl);
+		if (ret) {
+			dev_err(dev, "Failed to request soundwire wake irq\n");
+			goto err_init;
+		}
+	}
+
 	wait_for_completion_timeout(&ctrl->enumeration,
 				    msecs_to_jiffies(TIMEOUT_MS));
 	ret = qcom_swrm_register_dais(ctrl);
@@ -1589,6 +1632,18 @@ static int qcom_swrm_remove(struct platform_device *pdev)
 {
 	struct qcom_swrm_ctrl *ctrl = dev_get_drvdata(&pdev->dev);
 
+	/*
+	 * Mask interrupts to be sure no delayed work can be scheduler after
+	 * removing Soundwire bus master.
+	 */
+	if (ctrl->version < SWRM_VERSION_2_0_0)
+		ctrl->reg_write(ctrl, ctrl->reg_layout[SWRM_REG_INTERRUPT_MASK_ADDR],
+				0);
+	if (ctrl->mmio)
+		ctrl->reg_write(ctrl, ctrl->reg_layout[SWRM_REG_INTERRUPT_CPU_EN],
+				0);
+
+	cancel_delayed_work_sync(&ctrl->new_slave_work);
 	sdw_bus_master_delete(&ctrl->bus);
 	clk_disable_unprepare(ctrl->hclk);
 
-- 
2.34.1