[RFC] virtio-mmio: Update the device to OASIS spec version

Pawel Moll
Fri, 19 Dec 2014 18:38:04 -0000

This patch add a support for second version of the virtio-mmio device,
which follows OASIS "Virtual I/O Device (VIRTIO) Version 1.0"
specification.

Main changes:

1. The control register symbolic names use the new device/driver
   nomenclature rather than the old guest/host one.

2. The driver detect the device version (version 1 is the pre-OASIS
   spec, version 2 is compatible with fist revision of the OASIS spec)
   and drives the device accordingly.

3. New version uses direct addressing (64 bit address split into two
   low/high register) instead of the guest page size based one,
   and addresses each part of the queue (descriptors, available, used)
   separately.

4. The device activity is now explicitly triggered by writing to the
   "queue ready" register.

5. The platform device got a sysfs attribute with the version number.

6. Whole 64 bit features are properly handled now (both ways).

Signed-off-by: Pawel Moll <pawel.moll at arm.com>
---
I had the code typed for months now, but finally (just before
disappearing for the end-of-year break) got time to test it (and
fix the bugs), so I though I'd share it at least as RFC.

It's based on Linus tree still in merge window, but as far as I can
see all virtio changes have been already pulled, so I don't expect
any changes in rc1.

Tested with our custom models (*not* qemu).

Regards and till next year!

Pawel

 drivers/virtio/virtio_mmio.c | 132 +++++++++++++++++++++++++++----------------
 include/linux/virtio_mmio.h  |  46 +++++++++++----
 2 files changed, 120 insertions(+), 58 deletions(-)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 00d115b..d60675a 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -1,7 +1,7 @@
 /*
  * Virtio memory mapped device driver
  *
- * Copyright 2011, ARM Ltd.
+ * Copyright 2011-2014, ARM Ltd.
  *
  * This module allows virtio devices to be used over a virtual, memory mapped
  * platform device.
@@ -50,36 +50,6 @@
  *
  *
  *
- * Registers layout (all 32-bit wide):
- *
- * offset d. name             description
- * ------ -- ---------------- -----------------
- *
- * 0x000  R  MagicValue       Magic value "virt"
- * 0x004  R  Version          Device version (current max. 1)
- * 0x008  R  DeviceID         Virtio device ID
- * 0x00c  R  VendorID         Virtio vendor ID
- *
- * 0x010  R  HostFeatures     Features supported by the host
- * 0x014  W  HostFeaturesSel  Set of host features to access via HostFeatures
- *
- * 0x020  W  GuestFeatures    Features activated by the guest
- * 0x024  W  GuestFeaturesSel Set of activated features to set via
GuestFeatures
- * 0x028  W  GuestPageSize    Size of guest's memory page in bytes
- *
- * 0x030  W  QueueSel         Queue selector
- * 0x034  R  QueueNumMax      Maximum size of the currently selected queue
- * 0x038  W  QueueNum         Queue size for the currently selected queue
- * 0x03c  W  QueueAlign       Used Ring alignment for the current queue
- * 0x040  RW QueuePFN         PFN for the currently selected queue
- *
- * 0x050  W  QueueNotify      Queue notifier
- * 0x060  R  InterruptStatus  Interrupt status register
- * 0x064  W  InterruptACK     Interrupt acknowledge register
- * 0x070  RW Status           Device status register
- *
- * 0x100+ RW                  Device-specific configuration space
- *
  * Based on Virtio PCI driver by Anthony Liguori, copyright IBM Corp. 2007
  *
  * This work is licensed under the terms of the GNU GPL, version 2 or later.
@@ -145,11 +115,16 @@ struct virtio_mmio_vq_info {
 static u64 vm_get_features(struct virtio_device *vdev)
 {
 	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
+	u64 features;
+
+	writel(1, vm_dev->base + VIRTIO_MMIO_DEVICE_FEATURES_SEL);
+	features = readl(vm_dev->base + VIRTIO_MMIO_DEVICE_FEATURES);
+	features <<= 32;

-	/* TODO: Features > 32 bits */
-	writel(0, vm_dev->base + VIRTIO_MMIO_HOST_FEATURES_SEL);
+	writel(0, vm_dev->base + VIRTIO_MMIO_DEVICE_FEATURES_SEL);
+	features |= readl(vm_dev->base + VIRTIO_MMIO_DEVICE_FEATURES);

-	return readl(vm_dev->base + VIRTIO_MMIO_HOST_FEATURES);
+	return features;
 }

 static int vm_finalize_features(struct virtio_device *vdev)
@@ -159,11 +134,13 @@ static int vm_finalize_features(struct virtio_device
*vdev)
 	/* Give virtio_ring a chance to accept features. */
 	vring_transport_features(vdev);

-	/* Make sure we don't have any features > 32 bits! */
-	BUG_ON((u32)vdev->features != vdev->features);
+	writel(1, vm_dev->base + VIRTIO_MMIO_DRIVER_FEATURES_SEL);
+	writel((vdev->features >> 32) & 0xffffffff,
+			vm_dev->base + VIRTIO_MMIO_DRIVER_FEATURES);

-	writel(0, vm_dev->base + VIRTIO_MMIO_GUEST_FEATURES_SEL);
-	writel(vdev->features, vm_dev->base + VIRTIO_MMIO_GUEST_FEATURES);
+	writel(0, vm_dev->base + VIRTIO_MMIO_DRIVER_FEATURES_SEL);
+	writel(vdev->features & 0xffffffff,
+			vm_dev->base + VIRTIO_MMIO_DRIVER_FEATURES);

 	return 0;
 }
@@ -275,7 +252,12 @@ static void vm_del_vq(struct virtqueue *vq)

 	/* Select and deactivate the queue */
 	writel(index, vm_dev->base + VIRTIO_MMIO_QUEUE_SEL);
-	writel(0, vm_dev->base + VIRTIO_MMIO_QUEUE_PFN);
+	if (vm_dev->version == 1) {
+		writel(0, vm_dev->base + VIRTIO_MMIO_QUEUE_PFN);
+	} else {
+		writel(0, vm_dev->base + VIRTIO_MMIO_QUEUE_READY);
+		WARN_ON(readl(vm_dev->base + VIRTIO_MMIO_QUEUE_READY));
+	}

 	size = PAGE_ALIGN(vring_size(info->num, VIRTIO_MMIO_VRING_ALIGN));
 	free_pages_exact(info->queue, size);
@@ -312,7 +294,8 @@ static struct virtqueue *vm_setup_vq(struct virtio_device
*vdev, unsigned index,
 	writel(index, vm_dev->base + VIRTIO_MMIO_QUEUE_SEL);

 	/* Queue shouldn't already be set up. */
-	if (readl(vm_dev->base + VIRTIO_MMIO_QUEUE_PFN)) {
+	if (readl(vm_dev->base + (vm_dev->version == 1 ?
+			VIRTIO_MMIO_QUEUE_PFN : VIRTIO_MMIO_QUEUE_READY))) {
 		err = -ENOENT;
 		goto error_available;
 	}
@@ -358,10 +341,35 @@ static struct virtqueue *vm_setup_vq(struct virtio_device
*vdev, unsigned index,

 	/* Activate the queue */
 	writel(info->num, vm_dev->base + VIRTIO_MMIO_QUEUE_NUM);
-	writel(VIRTIO_MMIO_VRING_ALIGN,
-			vm_dev->base + VIRTIO_MMIO_QUEUE_ALIGN);
-	writel(virt_to_phys(info->queue) >> PAGE_SHIFT,
-			vm_dev->base + VIRTIO_MMIO_QUEUE_PFN);
+	if (vm_dev->version == 1) {
+		writel(VIRTIO_MMIO_VRING_ALIGN,
+				vm_dev->base + VIRTIO_MMIO_QUEUE_ALIGN);
+		writel(virt_to_phys(info->queue) >> PAGE_SHIFT,
+				vm_dev->base + VIRTIO_MMIO_QUEUE_PFN);
+	} else {
+		uint64_t addr = virt_to_phys(info->queue);
+
+		writel(addr & 0xffffffff,
+				vm_dev->base + VIRTIO_MMIO_QUEUE_DESC_LOW);
+		writel((addr >> 32) & 0xffffffff,
+				vm_dev->base + VIRTIO_MMIO_QUEUE_DESC_HIGH);
+
+		addr += info->num * sizeof(struct vring_desc);
+		writel(addr & 0xffffffff,
+				vm_dev->base + VIRTIO_MMIO_QUEUE_AVAIL_LOW);
+		writel((addr >> 32) & 0xffffffff,
+				vm_dev->base + VIRTIO_MMIO_QUEUE_AVAIL_HIGH);
+
+		addr += sizeof(struct vring_avail) + info->num * sizeof(__u16);
+		addr += VIRTIO_MMIO_VRING_ALIGN - 1;
+		addr &= ~(VIRTIO_MMIO_VRING_ALIGN - 1);
+		writel(addr & 0xffffffff,
+				vm_dev->base + VIRTIO_MMIO_QUEUE_USED_LOW);
+		writel((addr >> 32) & 0xffffffff,
+				vm_dev->base + VIRTIO_MMIO_QUEUE_USED_HIGH);
+
+		writel(1, vm_dev->base + VIRTIO_MMIO_QUEUE_READY);
+	}

 	/* Create the vring */
 	vq = vring_new_virtqueue(index, info->num, VIRTIO_MMIO_VRING_ALIGN, vdev,
@@ -381,7 +389,12 @@ static struct virtqueue *vm_setup_vq(struct virtio_device
*vdev, unsigned index,
 	return vq;

 error_new_virtqueue:
-	writel(0, vm_dev->base + VIRTIO_MMIO_QUEUE_PFN);
+	if (vm_dev->version == 1) {
+		writel(0, vm_dev->base + VIRTIO_MMIO_QUEUE_PFN);
+	} else {
+		writel(0, vm_dev->base + VIRTIO_MMIO_QUEUE_READY);
+		WARN_ON(readl(vm_dev->base + VIRTIO_MMIO_QUEUE_READY));
+	}
 	free_pages_exact(info->queue, size);
 error_alloc_pages:
 	kfree(info);
@@ -439,6 +452,18 @@ static const struct virtio_config_ops
virtio_mmio_config_ops = {

 /* Platform device */

+static ssize_t vm_dev_attr_version_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct virtio_mmio_device *vm_dev = platform_get_drvdata(pdev);
+
+	return snprintf(buf, PAGE_SIZE, "%lu", vm_dev->version);
+}
+
+static struct device_attribute vm_dev_attr_version +		__ATTR(version, S_IRUGO,
vm_dev_attr_version_show, NULL);
+
 static int virtio_mmio_probe(struct platform_device *pdev)
 {
 	struct virtio_mmio_device *vm_dev;
@@ -476,16 +501,26 @@ static int virtio_mmio_probe(struct platform_device *pdev)

 	/* Check device version */
 	vm_dev->version = readl(vm_dev->base + VIRTIO_MMIO_VERSION);
-	if (vm_dev->version != 1) {
+	if (vm_dev->version < 1 || vm_dev->version > 2) {
 		dev_err(&pdev->dev, "Version %ld not supported!\n",
 				vm_dev->version);
 		return -ENXIO;
 	}

 	vm_dev->vdev.id.device = readl(vm_dev->base + VIRTIO_MMIO_DEVICE_ID);
+	if (vm_dev->vdev.id.device == 0) {
+		/*
+		 * ID 0 means a dummy (placeholder) device, skip quietly
+		 * (as in: no error) with no further actions
+		 */
+		return 0;
+	}
 	vm_dev->vdev.id.vendor = readl(vm_dev->base + VIRTIO_MMIO_VENDOR_ID);

-	writel(PAGE_SIZE, vm_dev->base + VIRTIO_MMIO_GUEST_PAGE_SIZE);
+	if (vm_dev->version == 1)
+		writel(PAGE_SIZE, vm_dev->base + VIRTIO_MMIO_GUEST_PAGE_SIZE);
+
+	device_create_file(&pdev->dev, &vm_dev_attr_version);

 	platform_set_drvdata(pdev, vm_dev);

@@ -496,7 +531,8 @@ static int virtio_mmio_remove(struct platform_device *pdev)
 {
 	struct virtio_mmio_device *vm_dev = platform_get_drvdata(pdev);

-	unregister_virtio_device(&vm_dev->vdev);
+	if (vm_dev)
+		unregister_virtio_device(&vm_dev->vdev);

 	return 0;
 }
diff --git a/include/linux/virtio_mmio.h b/include/linux/virtio_mmio.h
index 5c7b6f0..d5f3634 100644
--- a/include/linux/virtio_mmio.h
+++ b/include/linux/virtio_mmio.h
@@ -51,21 +51,22 @@
 /* Virtio vendor ID - Read Only */
 #define VIRTIO_MMIO_VENDOR_ID		0x00c

-/* Bitmask of the features supported by the host
+/* Bitmask of the features supported by the device (host)
  * (32 bits per set) - Read Only */
-#define VIRTIO_MMIO_HOST_FEATURES	0x010
+#define VIRTIO_MMIO_DEVICE_FEATURES	0x010

-/* Host features set selector - Write Only */
-#define VIRTIO_MMIO_HOST_FEATURES_SEL	0x014
+/* Device (host) features set selector - Write Only */
+#define VIRTIO_MMIO_DEVICE_FEATURES_SEL	0x014

-/* Bitmask of features activated by the guest
+/* Bitmask of features activated by the driver (guest)
  * (32 bits per set) - Write Only */
-#define VIRTIO_MMIO_GUEST_FEATURES	0x020
+#define VIRTIO_MMIO_DRIVER_FEATURES	0x020

 /* Activated features set selector - Write Only */
-#define VIRTIO_MMIO_GUEST_FEATURES_SEL	0x024
+#define VIRTIO_MMIO_DRIVER_FEATURES_SEL	0x024

-/* Guest's memory page size in bytes - Write Only */
+/* Guest's memory page size in bytes - Write Only
+ * LEGACY DEVICES ONLY! */
 #define VIRTIO_MMIO_GUEST_PAGE_SIZE	0x028

 /* Queue selector - Write Only */
@@ -77,12 +78,18 @@
 /* Queue size for the currently selected queue - Write Only */
 #define VIRTIO_MMIO_QUEUE_NUM		0x038

-/* Used Ring alignment for the currently selected queue - Write Only */
+/* Used Ring alignment for the currently selected queue - Write Only
+ * LEGACY DEVICES ONLY! */
 #define VIRTIO_MMIO_QUEUE_ALIGN		0x03c

-/* Guest's PFN for the currently selected queue - Read Write */
+/* Guest's PFN for the currently selected queue - Read Write
+ * LEGACY DEVICES ONLY! */
 #define VIRTIO_MMIO_QUEUE_PFN		0x040

+/* Ready bit for the currently selected queue - Read Write
+ * NOT FOR LEGACY DEVICES! */
+#define VIRTIO_MMIO_QUEUE_READY		0x044
+
 /* Queue notifier - Write Only */
 #define VIRTIO_MMIO_QUEUE_NOTIFY	0x050

@@ -95,6 +102,25 @@
 /* Device status register - Read Write */
 #define VIRTIO_MMIO_STATUS		0x070

+/* Selected queue's Descriptor Table address, 64 bits in two halves
+ * NOT FOR LEGACY DEVICES! */
+#define VIRTIO_MMIO_QUEUE_DESC_LOW	0x080
+#define VIRTIO_MMIO_QUEUE_DESC_HIGH	0x084
+
+/* Selected queue's Available Ring address, 64 bits in two halves
+ * NOT FOR LEGACY DEVICES! */
+#define VIRTIO_MMIO_QUEUE_AVAIL_LOW	0x090
+#define VIRTIO_MMIO_QUEUE_AVAIL_HIGH	0x094
+
+/* Selected queue's Used Ring address, 64 bits in two halves
+ * NOT FOR LEGACY DEVICES! */
+#define VIRTIO_MMIO_QUEUE_USED_LOW	0x0a0
+#define VIRTIO_MMIO_QUEUE_USED_HIGH	0x0a4
+
+/* Configuration atomicity value
+ * NOT FOR LEGACY DEVICES! */
+#define VIRTIO_MMIO_CONFIG_GENERATION	0x0fc
+
 /* The config space is defined by each driver as
  * the per-driver configuration space - Read Write */
 #define VIRTIO_MMIO_CONFIG		0x100
--
2.1.0