soc: qcom: smsm: Support using mailbox interface

Add support for using the mbox interface instead of manually writing to
the syscon. With this change the driver will attempt to get the mailbox
first, and if that fails it will fall back to the existing way of using
qcom,ipc-* properties and converting to syscon.

Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Link: https://lore.kernel.org/r/20240606-smsm-mbox-v2-2-8abe6b5f01da@z3ntu.xyz
Signed-off-by: Bjorn Andersson <andersson@kernel.org>

drivers/soc/qcom/smsm.c

@@ -5,6 +5,7 @@
  */
 
 #include <linux/interrupt.h>
+#include <linux/mailbox_client.h>
 #include <linux/mfd/syscon.h>
 #include <linux/module.h>
 #include <linux/of_irq.h>
@@ -71,6 +72,7 @@ struct smsm_host;
  * @lock:	spinlock for read-modify-write of the outgoing state
  * @entries:	context for each of the entries
  * @hosts:	context for each of the hosts
+ * @mbox_client: mailbox client handle
  */
 struct qcom_smsm {
 	struct device *dev;
@@ -88,6 +90,8 @@ struct qcom_smsm {
 
 	struct smsm_entry *entries;
 	struct smsm_host *hosts;
+
+	struct mbox_client mbox_client;
 };
 
 /**
@@ -120,11 +124,14 @@ struct smsm_entry {
  * @ipc_regmap:	regmap for outgoing interrupt
  * @ipc_offset:	offset in @ipc_regmap for outgoing interrupt
  * @ipc_bit:	bit in @ipc_regmap + @ipc_offset for outgoing interrupt
+ * @mbox_chan:	apcs ipc mailbox channel handle
  */
 struct smsm_host {
 	struct regmap *ipc_regmap;
 	int ipc_offset;
 	int ipc_bit;
+
+	struct mbox_chan *mbox_chan;
 };
 
 /**
@@ -172,7 +179,13 @@ static int smsm_update_bits(void *data, u32 mask, u32 value)
 		hostp = &smsm->hosts[host];
 
 		val = readl(smsm->subscription + host);
-		if (val & changes && hostp->ipc_regmap) {
+		if (!(val & changes))
+			continue;
+
+		if (hostp->mbox_chan) {
+			mbox_send_message(hostp->mbox_chan, NULL);
+			mbox_client_txdone(hostp->mbox_chan, 0);
+		} else if (hostp->ipc_regmap) {
 			regmap_write(hostp->ipc_regmap,
 				     hostp->ipc_offset,
 				     BIT(hostp->ipc_bit));
@@ -352,6 +365,28 @@ static const struct irq_domain_ops smsm_irq_ops = {
 	.xlate = irq_domain_xlate_twocell,
 };
 
+/**
+ * smsm_parse_mbox() - requests an mbox channel
+ * @smsm:	smsm driver context
+ * @host_id:	index of the remote host to be resolved
+ *
+ * Requests the desired channel using the mbox interface which is needed for
+ * sending the outgoing interrupts to a remove hosts - identified by @host_id.
+ */
+static int smsm_parse_mbox(struct qcom_smsm *smsm, unsigned int host_id)
+{
+	struct smsm_host *host = &smsm->hosts[host_id];
+	int ret = 0;
+
+	host->mbox_chan = mbox_request_channel(&smsm->mbox_client, host_id);
+	if (IS_ERR(host->mbox_chan)) {
+		ret = PTR_ERR(host->mbox_chan);
+		host->mbox_chan = NULL;
+	}
+
+	return ret;
+}
+
 /**
  * smsm_parse_ipc() - parses a qcom,ipc-%d device tree property
  * @smsm:	smsm driver context
@@ -521,8 +556,16 @@ static int qcom_smsm_probe(struct platform_device *pdev)
 			     "qcom,local-host",
 			     &smsm->local_host);
 
+	smsm->mbox_client.dev = &pdev->dev;
+	smsm->mbox_client.knows_txdone = true;
+
 	/* Parse the host properties */
 	for (id = 0; id < smsm->num_hosts; id++) {
+		/* Try using mbox interface first, otherwise fall back to syscon */
+		ret = smsm_parse_mbox(smsm, id);
+		if (!ret)
+			continue;
+
 		ret = smsm_parse_ipc(smsm, id);
 		if (ret < 0)
 			goto out_put;
@@ -609,6 +652,9 @@ static int qcom_smsm_probe(struct platform_device *pdev)
 
 	qcom_smem_state_unregister(smsm->state);
 out_put:
+	for (id = 0; id < smsm->num_hosts; id++)
+		mbox_free_channel(smsm->hosts[id].mbox_chan);
+
 	of_node_put(local_node);
 	return ret;
 }
@@ -622,6 +668,9 @@ static void qcom_smsm_remove(struct platform_device *pdev)
 		if (smsm->entries[id].domain)
 			irq_domain_remove(smsm->entries[id].domain);
 
+	for (id = 0; id < smsm->num_hosts; id++)
+		mbox_free_channel(smsm->hosts[id].mbox_chan);
+
 	qcom_smem_state_unregister(smsm->state);
 }