rpmsg: qcom_smd: Access APCS through mailbox framework

Attempt to acquire the APCS IPC through the mailbox framework and fall
back to the old syscon based approach, to allow us to move away from
using the syscon.

Reviewed-by: Arun Kumar Neelakantam <[e-mail]>
Signed-off-by: Bjorn Andersson <[e-mail]>

Documentation/devicetree/bindings/soc/qcom/qcom,smd.txt

···
 	Definition: should specify the IRQ used by the remote processor to
 		    signal this processor about communication related updates
 
-- qcom,ipc:
+- mboxes:
 	Usage: required
+	Value type: <prop-encoded-array>
+	Definition: reference to the associated doorbell in APCS, as described
+		    in mailbox/mailbox.txt
+
+- qcom,ipc:
+	Usage: required, unless mboxes is specified
 	Value type: <prop-encoded-array>
 	Definition: three entries specifying the outgoing ipc bit used for
 		    signaling the remote processor:

drivers/rpmsg/Kconfig

···
 
 config RPMSG_QCOM_SMD
 	tristate "Qualcomm Shared Memory Driver (SMD)"
+	depends on MAILBOX
 	depends on QCOM_SMEM
 	select RPMSG
 	help

drivers/rpmsg/qcom_smd.c

···
 
 #include <linux/interrupt.h>
 #include <linux/io.h>
+#include <linux/mailbox_client.h>
 #include <linux/mfd/syscon.h>
 #include <linux/module.h>
 #include <linux/of_irq.h>
···
  * @ipc_regmap:		regmap handle holding the outgoing ipc register
  * @ipc_offset:		offset within @ipc_regmap of the register for ipc
  * @ipc_bit:		bit in the register at @ipc_offset of @ipc_regmap
+ * @mbox_client:	mailbox client handle
+ * @mbox_chan:		apcs ipc mailbox channel handle
  * @channels:		list of all channels detected on this edge
  * @channels_lock:	guard for modifications of @channels
  * @allocated:		array of bitmaps representing already allocated channels
···
 	struct regmap *ipc_regmap;
 	int ipc_offset;
 	int ipc_bit;
+
+	struct mbox_client mbox_client;
+	struct mbox_chan *mbox_chan;
 
 	struct list_head channels;
 	spinlock_t channels_lock;
···
 {
 	struct qcom_smd_edge *edge = channel->edge;
 
-	regmap_write(edge->ipc_regmap, edge->ipc_offset, BIT(edge->ipc_bit));
+	if (edge->mbox_chan) {
+		/*
+		 * We can ignore a failing mbox_send_message() as the only
+		 * possible cause is that the FIFO in the framework is full of
+		 * other writes to the same bit.
+		 */
+		mbox_send_message(edge->mbox_chan, NULL);
+		mbox_client_txdone(edge->mbox_chan, 0);
+	} else {
+		regmap_write(edge->ipc_regmap, edge->ipc_offset, BIT(edge->ipc_bit));
+	}
 }
 
 /*
···
 	key = "qcom,remote-pid";
 	of_property_read_u32(node, key, &edge->remote_pid);
 
-	syscon_np = of_parse_phandle(node, "qcom,ipc", 0);
-	if (!syscon_np) {
-		dev_err(dev, "no qcom,ipc node\n");
-		return -ENODEV;
-	}
+	edge->mbox_client.dev = dev;
+	edge->mbox_client.knows_txdone = true;
+	edge->mbox_chan = mbox_request_channel(&edge->mbox_client, 0);
+	if (IS_ERR(edge->mbox_chan)) {
+		if (PTR_ERR(edge->mbox_chan) != -ENODEV)
+			return PTR_ERR(edge->mbox_chan);
 
-	edge->ipc_regmap = syscon_node_to_regmap(syscon_np);
-	if (IS_ERR(edge->ipc_regmap))
-		return PTR_ERR(edge->ipc_regmap);
+		edge->mbox_chan = NULL;
 
-	key = "qcom,ipc";
-	ret = of_property_read_u32_index(node, key, 1, &edge->ipc_offset);
-	if (ret < 0) {
-		dev_err(dev, "no offset in %s\n", key);
-		return -EINVAL;
-	}
+		syscon_np = of_parse_phandle(node, "qcom,ipc", 0);
+		if (!syscon_np) {
+			dev_err(dev, "no qcom,ipc node\n");
+			return -ENODEV;
+		}
 
-	ret = of_property_read_u32_index(node, key, 2, &edge->ipc_bit);
-	if (ret < 0) {
-		dev_err(dev, "no bit in %s\n", key);
-		return -EINVAL;
+		edge->ipc_regmap = syscon_node_to_regmap(syscon_np);
+		if (IS_ERR(edge->ipc_regmap))
+			return PTR_ERR(edge->ipc_regmap);
+
+		key = "qcom,ipc";
+		ret = of_property_read_u32_index(node, key, 1, &edge->ipc_offset);
+		if (ret < 0) {
+			dev_err(dev, "no offset in %s\n", key);
+			return -EINVAL;
+		}
+
+		ret = of_property_read_u32_index(node, key, 2, &edge->ipc_bit);
+		if (ret < 0) {
+			dev_err(dev, "no bit in %s\n", key);
+			return -EINVAL;
+		}
 	}
 
 	ret = of_property_read_string(node, "label", &edge->name);
···
 	return edge;
 
 unregister_dev:
+	if (!IS_ERR_OR_NULL(edge->mbox_chan))
+		mbox_free_channel(edge->mbox_chan);
+
 	device_unregister(&edge->dev);
 	return ERR_PTR(ret);
 }
···
 	if (ret)
 		dev_warn(&edge->dev, "can't remove smd device: %d\n", ret);
 
+	mbox_free_channel(edge->mbox_chan);
 	device_unregister(&edge->dev);
 
 	return 0;