[RFC PATCH 1/2] Add a new register offset let interrupt reason available

["john.liuli" <john.liuli@huawei.com>]

From: Li Liu <john.liuli@huawei.com>

Add a new register offset VIRTIO_MMIO_ISRMEM which help to
estblish a shared memory region between virtio-mmio driver
and qemu with two purposes:

1.Guest virtio-mmio driver can get the interrupt reason.
2.Check irqfd enabled or not to register different irq handler.

Signed-off-by: Li Liu <john.liuli@huawei.com>
---
 drivers/virtio/virtio_mmio.c |   21 ++++++++++++++++++++-
 include/linux/virtio_mmio.h  |    3 +++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index ef9a165..28ddb55 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -122,6 +122,8 @@ struct virtio_mmio_device {
 	/* a list of queues so we can dispatch IRQs */
 	spinlock_t lock;
 	struct list_head virtqueues;
+
+	uint8_t *isr_mem;
 };
 
 struct virtio_mmio_vq_info {
@@ -443,6 +445,7 @@ static int virtio_mmio_probe(struct platform_device *pdev)
 	struct virtio_mmio_device *vm_dev;
 	struct resource *mem;
 	unsigned long magic;
+	int err;
 
 	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	if (!mem)
@@ -481,6 +484,15 @@ static int virtio_mmio_probe(struct platform_device *pdev)
 		return -ENXIO;
 	}
 
+	vm_dev->isr_mem = alloc_pages_exact(PAGE_SIZE, GFP_KERNEL|__GFP_ZERO);
+	if (vm_dev->isr_mem == NULL) {
+		dev_err(&pdev->dev, "Allocate isr memory failed!\n");
+		return -ENOMEM;
+	}
+
+	writel(virt_to_phys(vm_dev->isr_mem),
+	       vm_dev->base + VIRTIO_MMIO_ISRMEM);
+
 	vm_dev->vdev.id.device = readl(vm_dev->base + VIRTIO_MMIO_DEVICE_ID);
 	vm_dev->vdev.id.vendor = readl(vm_dev->base + VIRTIO_MMIO_VENDOR_ID);
 
@@ -488,13 +500,20 @@ static int virtio_mmio_probe(struct platform_device *pdev)
 
 	platform_set_drvdata(pdev, vm_dev);
 
-	return register_virtio_device(&vm_dev->vdev);
+	err = register_virtio_device(&vm_dev->vdev);
+	if (err) {
+		free_pages_exact(vm_dev->isr_mem, PAGE_SIZE);
+		vm_dev->isr_mem = NULL;
+	}
+
+	return err;
 }
 
 static int virtio_mmio_remove(struct platform_device *pdev)
 {
 	struct virtio_mmio_device *vm_dev = platform_get_drvdata(pdev);
 
+	free_pages_exact(vm_dev->isr_mem, PAGE_SIZE);
 	unregister_virtio_device(&vm_dev->vdev);
 
 	return 0;
diff --git a/include/linux/virtio_mmio.h b/include/linux/virtio_mmio.h
index 5c7b6f0..b1e3ec7 100644
--- a/include/linux/virtio_mmio.h
+++ b/include/linux/virtio_mmio.h
@@ -95,6 +95,9 @@
 /* Device status register - Read Write */
 #define VIRTIO_MMIO_STATUS		0x070
 
+/* Allocate ISRMEM for interrupt reason - Write Only */
+#define VIRTIO_MMIO_ISRMEM		0x080
+
 /* The config space is defined by each driver as
  * the per-driver configuration space - Read Write */
 #define VIRTIO_MMIO_CONFIG		0x100
-- 
1.7.9.5