qcom: apr: Make apr callbacks in non-atomic context

APR communication with DSP is not atomic in nature.
Its request-response type. Trying to pretend that these are atomic
and invoking apr client callbacks directly under atomic/irq context has
endless issues with soundcard. It makes more sense to convert these
to nonatomic calls. This also coverts all the dais to be nonatomic.

All the callbacks are now invoked as part of rx work queue.
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/soc/qcom/apr.c

@@ -8,6 +8,7 @@
 #include <linux/spinlock.h>
 #include <linux/idr.h>
 #include <linux/slab.h>
+#include <linux/workqueue.h>
 #include <linux/of_device.h>
 #include <linux/soc/qcom/apr.h>
 #include <linux/rpmsg.h>
@@ -17,8 +18,18 @@ struct apr {
 	struct rpmsg_endpoint *ch;
 	struct device *dev;
 	spinlock_t svcs_lock;
+	spinlock_t rx_lock;
 	struct idr svcs_idr;
 	int dest_domain_id;
+	struct workqueue_struct *rxwq;
+	struct work_struct rx_work;
+	struct list_head rx_list;
+};
+
+struct apr_rx_buf {
+	struct list_head node;
+	int len;
+	uint8_t buf[];
 };
 
 /**
@@ -62,11 +73,7 @@ static int apr_callback(struct rpmsg_device *rpdev, void *buf,
 				  int len, void *priv, u32 addr)
 {
 	struct apr *apr = dev_get_drvdata(&rpdev->dev);
-	uint16_t hdr_size, msg_type, ver, svc_id;
-	struct apr_device *svc = NULL;
-	struct apr_driver *adrv = NULL;
-	struct apr_resp_pkt resp;
-	struct apr_hdr *hdr;
+	struct apr_rx_buf *abuf;
 	unsigned long flags;
 
 	if (len <= APR_HDR_SIZE) {
@@ -75,6 +82,34 @@ static int apr_callback(struct rpmsg_device *rpdev, void *buf,
 		return -EINVAL;
 	}
 
+	abuf = kzalloc(sizeof(*abuf) + len, GFP_ATOMIC);
+	if (!abuf)
+		return -ENOMEM;
+
+	abuf->len = len;
+	memcpy(abuf->buf, buf, len);
+
+	spin_lock_irqsave(&apr->rx_lock, flags);
+	list_add_tail(&abuf->node, &apr->rx_list);
+	spin_unlock_irqrestore(&apr->rx_lock, flags);
+
+	queue_work(apr->rxwq, &apr->rx_work);
+
+	return 0;
+}
+
+
+static int apr_do_rx_callback(struct apr *apr, struct apr_rx_buf *abuf)
+{
+	uint16_t hdr_size, msg_type, ver, svc_id;
+	struct apr_device *svc = NULL;
+	struct apr_driver *adrv = NULL;
+	struct apr_resp_pkt resp;
+	struct apr_hdr *hdr;
+	unsigned long flags;
+	void *buf = abuf->buf;
+	int len = abuf->len;
+
 	hdr = buf;
 	ver = APR_HDR_FIELD_VER(hdr->hdr_field);
 	if (ver > APR_PKT_VER + 1)
@@ -132,6 +167,23 @@ static int apr_callback(struct rpmsg_device *rpdev, void *buf,
 	return 0;
 }
 
+static void apr_rxwq(struct work_struct *work)
+{
+	struct apr *apr = container_of(work, struct apr, rx_work);
+	struct apr_rx_buf *abuf, *b;
+	unsigned long flags;
+
+	if (!list_empty(&apr->rx_list)) {
+		list_for_each_entry_safe(abuf, b, &apr->rx_list, node) {
+			apr_do_rx_callback(apr, abuf);
+			spin_lock_irqsave(&apr->rx_lock, flags);
+			list_del(&abuf->node);
+			spin_unlock_irqrestore(&apr->rx_lock, flags);
+			kfree(abuf);
+		}
+	}
+}
+
 static int apr_device_match(struct device *dev, struct device_driver *drv)
 {
 	struct apr_device *adev = to_apr_device(dev);
@@ -285,6 +337,14 @@ static int apr_probe(struct rpmsg_device *rpdev)
 	dev_set_drvdata(dev, apr);
 	apr->ch = rpdev->ept;
 	apr->dev = dev;
+	apr->rxwq = create_singlethread_workqueue("qcom_apr_rx");
+	if (!apr->rxwq) {
+		dev_err(apr->dev, "Failed to start Rx WQ\n");
+		return -ENOMEM;
+	}
+	INIT_WORK(&apr->rx_work, apr_rxwq);
+	INIT_LIST_HEAD(&apr->rx_list);
+	spin_lock_init(&apr->rx_lock);
 	spin_lock_init(&apr->svcs_lock);
 	idr_init(&apr->svcs_idr);
 	of_register_apr_devices(dev);
@@ -303,7 +363,11 @@ static int apr_remove_device(struct device *dev, void *null)
 
 static void apr_remove(struct rpmsg_device *rpdev)
 {
+	struct apr *apr = dev_get_drvdata(&rpdev->dev);
+
 	device_for_each_child(&rpdev->dev, NULL, apr_remove_device);
+	flush_workqueue(apr->rxwq);
+	destroy_workqueue(apr->rxwq);
 }
 
 /*