slim-msm: Synchronize SSR callbacks

Subsystem will restart within short timeframe.
Synchronise subsytem up/down callback notifications
to avoid functionality failures.
Use mutex locks to achieve synchronization.

Change-Id: I5881c7d468507bb8402a2e9f8178b9c31e57e8a5
Signed-off-by: Dilip Kota <dkota@codeaurora.org>

drivers/slimbus/slim-msm-ngd.c

@@ -1266,11 +1266,13 @@ static void ngd_adsp_down(struct work_struct *work)
 	struct slim_controller *ctrl = &dev->ctrl;
 	struct slim_device *sbdev;
 
+	mutex_lock(&dev->ssr_lock);
 	ngd_slim_enable(dev, false);
 	/* device up should be called again after SSR */
 	list_for_each_entry(sbdev, &ctrl->devs, dev_list)
 		slim_report_absent(sbdev);
 	SLIM_INFO(dev, "SLIM ADSP SSR (DOWN) done\n");
+	mutex_unlock(&dev->ssr_lock);
 }
 
 static void ngd_adsp_up(struct work_struct *work)
@@ -1279,7 +1281,9 @@ static void ngd_adsp_up(struct work_struct *work)
 		container_of(work, struct msm_slim_qmi, ssr_up);
 	struct msm_slim_ctrl *dev =
 		container_of(qmi, struct msm_slim_ctrl, qmi);
+	mutex_lock(&dev->ssr_lock);
 	ngd_slim_enable(dev, true);
+	mutex_unlock(&dev->ssr_lock);
 }
 
 static ssize_t show_mask(struct device *device, struct device_attribute *attr,
@@ -1433,6 +1437,7 @@ static int __devinit ngd_slim_probe(struct platform_device *pdev)
 	init_completion(&dev->ctrl_up);
 	mutex_init(&dev->tx_lock);
 	mutex_init(&dev->tx_buf_lock);
+	mutex_init(&dev->ssr_lock);
 	spin_lock_init(&dev->rx_lock);
 	dev->ee = 1;
 	dev->irq = irq->start;

drivers/slimbus/slim-msm.h

@@ -256,6 +256,7 @@ struct msm_slim_ctrl {
 	struct clk		*hclk;
 	struct mutex		tx_lock;
 	struct mutex		tx_buf_lock;
+	struct mutex		ssr_lock;
 	u8			pgdla;
 	enum msm_slim_msgq	use_rx_msgqs;
 	enum msm_slim_msgq	use_tx_msgqs;