[PATCH v9 5/9] scsi: ibmvfc: add interrupt routine for asynchronous sub CRQ

[Tyrel Datwyler <tyreld@linux.ibm.com>]

From: Dave Marquardt <davemarq@linux.ibm.com>

Add ibmvfc_interrupt_async_subq(), an IRQ handler dedicated to
asynchronous sub-CRQ events from the adapter. The handler disables
the sub-CRQ IRQ and then calls ibmvfc_drain_async_subq() to consume
all pending entries before re-enabling interrupts. The handler is
marked as __maybe_unused until a later patch when it is used.

ibmvfc_drain_async_subq() holds the per-queue q_lock while
processing. It loops over available CRQ entries via ibmvfc_next_scrq(),
wrapping each in a typed struct ibmvfc_async_crq_event and dispatching
it to ibmvfc_handle_async(), then clears the valid bit and issues a
write barrier. After draining, it re-enables the sub-CRQ IRQ and performs
one final check for a newly arrived entry to close the IRQ-enable race;
if one is found it is processed before exiting the loop.

Signed-off-by: Dave Marquardt <davemarq@linux.ibm.com>
Acked-by: Tyrel Datwyler <tyreld@linux.ibm.com>
---
 drivers/scsi/ibmvscsi/ibmvfc-core.c | 54 +++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/drivers/scsi/ibmvscsi/ibmvfc-core.c b/drivers/scsi/ibmvscsi/ibmvfc-core.c
index daec81f48857..553fca31cb3a 100644
--- a/drivers/scsi/ibmvscsi/ibmvfc-core.c
+++ b/drivers/scsi/ibmvscsi/ibmvfc-core.c
@@ -4376,6 +4376,60 @@ static struct ibmvfc_crq *ibmvfc_next_scrq(struct ibmvfc_queue *scrq)
 	return crq;
 }
 
+static void ibmvfc_drain_async_subq(struct ibmvfc_queue *scrq)
+{
+	struct ibmvfc_host *vhost = scrq->vhost;
+	unsigned long flags;
+	struct ibmvfc_crq *crq;
+	int done = 0;
+
+	spin_lock_irqsave(vhost->host->host_lock, flags);
+	spin_lock(scrq->q_lock);
+	while (!done) {
+		while ((crq = ibmvfc_next_scrq(scrq)) != NULL) {
+			struct ibmvfc_async_crq_event ae = {
+				.type = IBMVFC_ASYNC_CRQ_SUB,
+				.subq = *(struct ibmvfc_async_sub_crq *)crq,
+			};
+			ibmvfc_handle_async(&ae, scrq->vhost);
+			crq->valid = 0;
+			wmb();	/* complete write */
+		}
+
+		ibmvfc_toggle_scrq_irq(scrq, 1);
+		crq = ibmvfc_next_scrq(scrq);
+		if (crq != NULL) {
+			struct ibmvfc_async_crq_event ae = {
+				.type = IBMVFC_ASYNC_CRQ_SUB,
+				.subq = *(struct ibmvfc_async_sub_crq *)crq,
+			};
+			ibmvfc_toggle_scrq_irq(scrq, 0);
+			ibmvfc_handle_async(&ae, scrq->vhost);
+			crq->valid = 0;
+			wmb();	/* complete write */
+		} else
+			done = 1;
+	}
+	spin_unlock(scrq->q_lock);
+	spin_unlock_irqrestore(vhost->host->host_lock, flags);
+}
+
+/**
+ * ibmvfc_interrupt_async_subq - Handle an async event from the adapter
+ * @irq:           interrupt request
+ * @scrq_instance: async subq
+ *
+ **/
+static irqreturn_t __maybe_unused ibmvfc_interrupt_async_subq(int irq, void *scrq_instance)
+{
+	struct ibmvfc_queue *scrq = (struct ibmvfc_queue *)scrq_instance;
+
+	ibmvfc_toggle_scrq_irq(scrq, 0);
+	ibmvfc_drain_async_subq(scrq);
+
+	return IRQ_HANDLED;
+}
+
 static void ibmvfc_drain_sub_crq(struct ibmvfc_queue *scrq)
 {
 	struct ibmvfc_crq *crq;
-- 
2.55.0