firmware: arm_scmi: Add support for platform to agent channel completion

On some systems the SCMI platform to agent(p2a) communication can be fully
interrupt driven. The notification(p2a) channel needs completion interrupt
to drive its notification queue at the platform. Without it, the platform
notification will not work as the platform will wait for agent indication
of clearing the channel via interrupt unlike few platforms which can poll
instead.

To support such systems, an optional unidirectional mailbox channel for
p2a reply communication. If the platform sets channel INTR flag set
indicating that it expects the agent to trigger the interrupt to acknowledge
the reciept of the notification or any p2a message, and the completion
interrupt channel is provided, send a mailbox message to the platform
after the p2a message is read and channel is freed to accept new
notifications or p2a messages.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/20240510-scmi-notify-v2-2-e994cf14ef86@nxp.com
Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_scmi/common.h

@@ -326,6 +326,7 @@ void shmem_clear_channel(struct scmi_shared_mem __iomem *shmem);
 bool shmem_poll_done(struct scmi_shared_mem __iomem *shmem,
 		     struct scmi_xfer *xfer);
 bool shmem_channel_free(struct scmi_shared_mem __iomem *shmem);
+bool shmem_channel_intr_enabled(struct scmi_shared_mem __iomem *shmem);
 
 /* declarations for message passing transports */
 struct scmi_msg_payld;

drivers/firmware/arm_scmi/mailbox.c

@@ -21,6 +21,7 @@
  * @cl: Mailbox Client
  * @chan: Transmit/Receive mailbox uni/bi-directional channel
  * @chan_receiver: Optional Receiver mailbox unidirectional channel
+ * @chan_platform_receiver: Optional Platform Receiver mailbox unidirectional channel
  * @cinfo: SCMI channel info
  * @shmem: Transmit/Receive shared memory area
  */
@@ -28,6 +29,7 @@ struct scmi_mailbox {
 	struct mbox_client cl;
 	struct mbox_chan *chan;
 	struct mbox_chan *chan_receiver;
+	struct mbox_chan *chan_platform_receiver;
 	struct scmi_chan_info *cinfo;
 	struct scmi_shared_mem __iomem *shmem;
 };
@@ -91,6 +93,8 @@ static bool mailbox_chan_available(struct device_node *of_node, int idx)
  *		 for replies on the a2p channel. Set as zero if not present.
  * @p2a_chan: A reference to the optional p2a channel.
  *	      Set as zero if not present.
+ * @p2a_rx_chan: A reference to the optional p2a completion channel.
+ *	      Set as zero if not present.
  *
  * At first, validate the transport configuration as described in terms of
  * 'mboxes' and 'shmem', then determin which mailbox channel indexes are
@@ -98,8 +102,8 @@ static bool mailbox_chan_available(struct device_node *of_node, int idx)
  *
  * Return: 0 on Success or error
  */
-static int mailbox_chan_validate(struct device *cdev,
+static int mailbox_chan_validate(struct device *cdev, int *a2p_rx_chan,
-				 int *a2p_rx_chan, int *p2a_chan)
+				 int *p2a_chan, int *p2a_rx_chan)
 {
 	int num_mb, num_sh, ret = 0;
 	struct device_node *np = cdev->of_node;
@@ -109,8 +113,9 @@ static int mailbox_chan_validate(struct device *cdev,
 	dev_dbg(cdev, "Found %d mboxes and %d shmems !\n", num_mb, num_sh);
 
 	/* Bail out if mboxes and shmem descriptors are inconsistent */
-	if (num_mb <= 0 || num_sh <= 0 || num_sh > 2 || num_mb > 3 ||
+	if (num_mb <= 0 || num_sh <= 0 || num_sh > 2 || num_mb > 4 ||
-	    (num_mb == 1 && num_sh != 1) || (num_mb == 3 && num_sh != 2)) {
+	    (num_mb == 1 && num_sh != 1) || (num_mb == 3 && num_sh != 2) ||
+	    (num_mb == 4 && num_sh != 2)) {
 		dev_warn(cdev,
 			 "Invalid channel descriptor for '%s' - mbs:%d  shm:%d\n",
 			 of_node_full_name(np), num_mb, num_sh);
@@ -139,6 +144,7 @@ static int mailbox_chan_validate(struct device *cdev,
 		case 1:
 			*a2p_rx_chan = 0;
 			*p2a_chan = 0;
+			*p2a_rx_chan = 0;
 			break;
 		case 2:
 			if (num_sh == 2) {
@@ -148,10 +154,17 @@ static int mailbox_chan_validate(struct device *cdev,
 				*a2p_rx_chan = 1;
 				*p2a_chan = 0;
 			}
+			*p2a_rx_chan = 0;
 			break;
 		case 3:
 			*a2p_rx_chan = 1;
 			*p2a_chan = 2;
+			*p2a_rx_chan = 0;
+			break;
+		case 4:
+			*a2p_rx_chan = 1;
+			*p2a_chan = 2;
+			*p2a_rx_chan = 3;
 			break;
 		}
 	}
@@ -166,12 +179,12 @@ static int mailbox_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
 	struct device *cdev = cinfo->dev;
 	struct scmi_mailbox *smbox;
 	struct device_node *shmem;
-	int ret, a2p_rx_chan, p2a_chan, idx = tx ? 0 : 1;
+	int ret, a2p_rx_chan, p2a_chan, p2a_rx_chan, idx = tx ? 0 : 1;
 	struct mbox_client *cl;
 	resource_size_t size;
 	struct resource res;
 
-	ret = mailbox_chan_validate(cdev, &a2p_rx_chan, &p2a_chan);
+	ret = mailbox_chan_validate(cdev, &a2p_rx_chan, &p2a_chan, &p2a_rx_chan);
 	if (ret)
 		return ret;
 
@@ -229,6 +242,17 @@ static int mailbox_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
 		}
 	}
 
+	if (!tx && p2a_rx_chan) {
+		smbox->chan_platform_receiver = mbox_request_channel(cl, p2a_rx_chan);
+		if (IS_ERR(smbox->chan_platform_receiver)) {
+			ret = PTR_ERR(smbox->chan_platform_receiver);
+			if (ret != -EPROBE_DEFER)
+				dev_err(cdev, "failed to request SCMI P2A Receiver mailbox\n");
+			return ret;
+		}
+	}
+
+
 	cinfo->transport_info = smbox;
 	smbox->cinfo = cinfo;
 
@@ -243,9 +267,11 @@ static int mailbox_chan_free(int id, void *p, void *data)
 	if (smbox && !IS_ERR(smbox->chan)) {
 		mbox_free_channel(smbox->chan);
 		mbox_free_channel(smbox->chan_receiver);
+		mbox_free_channel(smbox->chan_platform_receiver);
 		cinfo->transport_info = NULL;
 		smbox->chan = NULL;
 		smbox->chan_receiver = NULL;
+		smbox->chan_platform_receiver = NULL;
 		smbox->cinfo = NULL;
 	}
 
@@ -300,8 +326,27 @@ static void mailbox_fetch_notification(struct scmi_chan_info *cinfo,
 static void mailbox_clear_channel(struct scmi_chan_info *cinfo)
 {
 	struct scmi_mailbox *smbox = cinfo->transport_info;
+	struct mbox_chan *intr_chan;
+	int ret;
 
 	shmem_clear_channel(smbox->shmem);
+
+	if (!shmem_channel_intr_enabled(smbox->shmem))
+		return;
+
+	if (smbox->chan_platform_receiver)
+		intr_chan = smbox->chan_platform_receiver;
+	else if (smbox->chan)
+		intr_chan = smbox->chan;
+	else
+		return;
+
+	ret = mbox_send_message(intr_chan, NULL);
+	/* mbox_send_message returns non-negative value on success, so reset */
+	if (ret > 0)
+		ret = 0;
+
+	mbox_client_txdone(intr_chan, ret);
 }
 
 static bool

drivers/firmware/arm_scmi/shmem.c

@@ -128,3 +128,8 @@ bool shmem_channel_free(struct scmi_shared_mem __iomem *shmem)
 	return (ioread32(&shmem->channel_status) &
 			SCMI_SHMEM_CHAN_STAT_CHANNEL_FREE);
 }
+
+bool shmem_channel_intr_enabled(struct scmi_shared_mem __iomem *shmem)
+{
+	return ioread32(&shmem->flags) & SCMI_SHMEM_FLAG_INTR_ENABLED;
+}