[PATCH v4 2/2] firmware: arm_scmi: Augment SMC/HVC to allow optional interrupt

[Jim Quinlan <jim2101024@gmail.com>]

The SMC/HVC SCMI transport is modified to allow the completion of an SCMI
message to be indicated by an interrupt rather than the return of the smc
call.  This accommodates the existing behavior of the BrcmSTB SCMI
"platform" whose SW is already out in the field and cannot be changed.

Signed-off-by: Jim Quinlan <jim2101024@gmail.com>
---
 drivers/firmware/arm_scmi/smc.c | 38 ++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/arm_scmi/smc.c b/drivers/firmware/arm_scmi/smc.c
index 82a82a5dc86a..fd41d436e34b 100644
--- a/drivers/firmware/arm_scmi/smc.c
+++ b/drivers/firmware/arm_scmi/smc.c
@@ -9,9 +9,11 @@
 #include <linux/arm-smccc.h>
 #include <linux/device.h>
 #include <linux/err.h>
+#include <linux/interrupt.h>
 #include <linux/mutex.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
+#include <linux/of_irq.h>
 #include <linux/slab.h>
 
 #include "common.h"
@@ -23,6 +25,8 @@
  * @shmem: Transmit/Receive shared memory area
  * @shmem_lock: Lock to protect access to Tx/Rx shared memory area
  * @func_id: smc/hvc call function id
+ * @irq: Optional; employed when platforms indicates msg completion by intr.
+ * @tx_complete: Optional, employed only when irq is valid.
  */
 
 struct scmi_smc {
@@ -30,8 +34,19 @@ struct scmi_smc {
 	struct scmi_shared_mem __iomem *shmem;
 	struct mutex shmem_lock;
 	u32 func_id;
+	int irq;
+	struct completion tx_complete;
 };
 
+static irqreturn_t smc_msg_done_isr(int irq, void *data)
+{
+	struct scmi_smc *scmi_info = data;
+
+	complete(&scmi_info->tx_complete);
+
+	return IRQ_HANDLED;
+}
+
 static bool smc_chan_available(struct device *dev, int idx)
 {
 	struct device_node *np = of_parse_phandle(dev->of_node, "shmem", 0);
@@ -51,7 +66,7 @@ static int smc_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
 	struct resource res;
 	struct device_node *np;
 	u32 func_id;
-	int ret;
+	int ret, irq = 0;
 
 	if (!tx)
 		return -ENODEV;
@@ -79,10 +94,29 @@ static int smc_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
 	if (ret < 0)
 		return ret;
 
+	/*
+	 * If there is an interrupt named "a2p", then the
+	 * service and completion of a message is signaled by an interrupt
+	 * rather than by the return of the SMC call.
+	 */
+	ret = of_irq_get_byname(cdev->of_node, "a2p");
+	if (ret > 0) {
+		irq = ret;
+		ret = devm_request_irq(dev, irq, smc_msg_done_isr,
+				       IRQF_NO_SUSPEND,
+				       dev_name(dev),
+				       scmi_info);
+		if (ret) {
+			dev_err(dev, "failed to setup SCMI smc irq\n");
+			return ret;
+		}
+		init_completion(&scmi_info->tx_complete);
+	}
 	scmi_info->func_id = func_id;
 	scmi_info->cinfo = cinfo;
 	mutex_init(&scmi_info->shmem_lock);
 	cinfo->transport_info = scmi_info;
+	scmi_info->irq = irq;
 
 	return 0;
 }
@@ -111,6 +145,8 @@ static int smc_send_message(struct scmi_chan_info *cinfo,
 	shmem_tx_prepare(scmi_info->shmem, xfer);
 
 	arm_smccc_1_1_invoke(scmi_info->func_id, 0, 0, 0, 0, 0, 0, 0, &res);
+	if (scmi_info->irq)
+		wait_for_completion(&scmi_info->tx_complete);
 	scmi_rx_callback(scmi_info->cinfo, shmem_read_header(scmi_info->shmem));
 
 	mutex_unlock(&scmi_info->shmem_lock);
-- 
2.17.1