[PATCH 2/2] virtio-mmio: Support multiple interrupts per device

[Jakub Sitnicki]

Some virtual devices, such as the virtio network device, can use multiple
virtqueues (or multiple pairs of virtqueues in the case of a vNIC). In such
case, when there are multiple vCPUs present, it is possible to process
virtqueue events in parallel. Each vCPU can service a subset of all
virtqueues when notified that there is work to carry out.

However, the current virtio-mmio transport implementation poses a
limitation. Only one vCPU can service notifications from any of the
virtqueues of a single virtio device. This is because a virtio-mmio device
driver supports registering just one interrupt per device. With such setup
we are not able to scale virtqueue event processing among vCPUs.

Now, with more than one IRQ resource registered for a virtio-mmio platform
device, we can address this limitation.

First, we request multiple IRQs when creating virtqueues for a device.

Then, map each virtqueue to one of the IRQs assigned to the device. The
mapping is done in a device type specific manner. For instance, a network
device will want each RX/TX virtqueue pair mapped to a different IRQ
line. Other device types might require a different mapping scheme. We
currently provide a mapping for virtio-net device type.

Finally, when handling an interrupt, we service only the virtqueues
associated with the IRQ line that triggered the event.

Signed-off-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
---
 drivers/virtio/virtio_mmio.c | 102 +++++++++++++++++++++++++++++++++++--------
 1 file changed, 83 insertions(+), 19 deletions(-)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 06a587b23542..180c51c27704 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -69,6 +69,7 @@
 #include <linux/spinlock.h>
 #include <linux/virtio.h>
 #include <linux/virtio_config.h>
+#include <uapi/linux/virtio_ids.h>
 #include <uapi/linux/virtio_mmio.h>
 #include <linux/virtio_ring.h>
 
@@ -93,6 +94,10 @@ struct virtio_mmio_device {
 	/* a list of queues so we can dispatch IRQs */
 	spinlock_t lock;
 	struct list_head virtqueues;
+
+	/* IRQ range allocated to the device */
+	unsigned int irq_base;
+	unsigned int num_irqs;
 };
 
 struct virtio_mmio_vq_info {
@@ -101,6 +106,9 @@ struct virtio_mmio_vq_info {
 
 	/* the list node for the virtqueues list */
 	struct list_head node;
+
+	/* IRQ mapped to virtqueue */
+	unsigned int irq;
 };
 
 
@@ -297,7 +305,7 @@ static bool vm_notify_with_data(struct virtqueue *vq)
 	return true;
 }
 
-/* Notify all virtqueues on an interrupt. */
+/* Notify all or some virtqueues on an interrupt. */
 static irqreturn_t vm_interrupt(int irq, void *opaque)
 {
 	struct virtio_mmio_device *vm_dev = opaque;
@@ -308,20 +316,31 @@ static irqreturn_t vm_interrupt(int irq, void *opaque)
 
 	/* Read and acknowledge interrupts */
 	status = readl(vm_dev->base + VIRTIO_MMIO_INTERRUPT_STATUS);
-	writel(status, vm_dev->base + VIRTIO_MMIO_INTERRUPT_ACK);
 
 	if (unlikely(status & VIRTIO_MMIO_INT_CONFIG)) {
+		writel(status & VIRTIO_MMIO_INT_CONFIG, vm_dev->base + VIRTIO_MMIO_INTERRUPT_ACK);
 		virtio_config_changed(&vm_dev->vdev);
 		ret = IRQ_HANDLED;
 	}
 
 	if (likely(status & VIRTIO_MMIO_INT_VRING)) {
+		writel(status & VIRTIO_MMIO_INT_VRING, vm_dev->base + VIRTIO_MMIO_INTERRUPT_ACK);
 		spin_lock_irqsave(&vm_dev->lock, flags);
 		list_for_each_entry(info, &vm_dev->virtqueues, node)
 			ret |= vring_interrupt(irq, info->vq);
 		spin_unlock_irqrestore(&vm_dev->lock, flags);
 	}
 
+	/* Notify only affected vrings if device uses multiple interrupts */
+	if (vm_dev->num_irqs > 1) {
+		spin_lock_irqsave(&vm_dev->lock, flags);
+		list_for_each_entry(info, &vm_dev->virtqueues, node) {
+			if (info->irq == irq)
+				ret |= vring_interrupt(irq, info->vq);
+		}
+		spin_unlock_irqrestore(&vm_dev->lock, flags);
+	}
+
 	return ret;
 }
 
@@ -356,11 +375,15 @@ static void vm_del_vqs(struct virtio_device *vdev)
 {
 	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
 	struct virtqueue *vq, *n;
+	int i, irq;
+
+	for (i = 0; i < vm_dev->num_irqs; i++) {
+		irq = vm_dev->irq_base + i;
+		devm_free_irq(&vdev->dev, irq, vm_dev);
+	}
 
 	list_for_each_entry_safe(vq, n, &vdev->vqs, list)
 		vm_del_vq(vq);
-
-	free_irq(platform_get_irq(vm_dev->pdev, 0), vm_dev);
 }
 
 static void vm_synchronize_cbs(struct virtio_device *vdev)
@@ -488,6 +511,18 @@ static struct virtqueue *vm_setup_vq(struct virtio_device *vdev, unsigned int in
 	return ERR_PTR(err);
 }
 
+/* Map virtqueue to zero-based interrupt number */
+static unsigned int vq2irq(const struct virtqueue *vq)
+{
+	switch (vq->vdev->id.device) {
+	case VIRTIO_ID_NET:
+		/* interrupt shared by rx/tx virtqueue pair */
+		return vq->index / 2;
+	default:
+		return 0;
+	}
+}
+
 static int vm_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
 		       struct virtqueue *vqs[],
 		       vq_callback_t *callbacks[],
@@ -496,19 +531,9 @@ static int vm_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
 		       struct irq_affinity *desc)
 {
 	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
-	int irq = platform_get_irq(vm_dev->pdev, 0);
-	int i, err, queue_idx = 0;
-
-	if (irq < 0)
-		return irq;
-
-	err = request_irq(irq, vm_interrupt, IRQF_SHARED,
-			dev_name(&vdev->dev), vm_dev);
-	if (err)
-		return err;
-
-	if (of_property_read_bool(vm_dev->pdev->dev.of_node, "wakeup-source"))
-		enable_irq_wake(irq);
+	struct virtio_mmio_vq_info *info;
+	int i, err, irq, nirqs, queue_idx = 0;
+	unsigned int irq_base = UINT_MAX;
 
 	for (i = 0; i < nvqs; ++i) {
 		if (!names[i]) {
@@ -519,12 +544,51 @@ static int vm_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
 		vqs[i] = vm_setup_vq(vdev, queue_idx++, callbacks[i], names[i],
 				     ctx ? ctx[i] : false);
 		if (IS_ERR(vqs[i])) {
-			vm_del_vqs(vdev);
-			return PTR_ERR(vqs[i]);
+			err = PTR_ERR(vqs[i]);
+			goto fail_vq;
 		}
 	}
 
+	nirqs = platform_irq_count(vm_dev->pdev);
+	if (nirqs < 0) {
+		err = nirqs;
+		goto fail_vq;
+	}
+
+	for (i = 0; i < nirqs; i++) {
+		irq = platform_get_irq(vm_dev->pdev, i);
+		if (irq < 0)
+			goto fail_irq;
+		if (irq < irq_base)
+			irq_base = irq;
+
+		err = devm_request_irq(&vdev->dev, irq, vm_interrupt,
+				       IRQF_SHARED, NULL, vm_dev);
+		if (err)
+			goto fail_irq;
+
+		if (of_property_read_bool(vm_dev->pdev->dev.of_node, "wakeup-source"))
+			enable_irq_wake(irq);
+	}
+
+	for (i = 0; i < nvqs; i++) {
+		irq = vq2irq(vqs[i]);
+		info = vqs[i]->priv;
+		info->irq = irq_base + (irq % nirqs);
+	}
+
+	vm_dev->irq_base = irq_base;
+	vm_dev->num_irqs = nirqs;
+
 	return 0;
+
+fail_irq:
+	while (i--)
+		devm_free_irq(&vdev->dev, irq_base + i, vm_dev);
+fail_vq:
+	vm_del_vqs(vdev);
+
+	return err;
 }
 
 static const char *vm_bus_name(struct virtio_device *vdev)

-- 
2.41.0