[PATCH v2 1/5] uio: Add hv_vmbus_client driver

[Saurabh Sengar]

Generic VMBus driver that can be dynamically bound, to any simple
low speed Hyper-V VMBus device. This driver supports single
channel and uses hypercall instead of monitor bits to interrupt
host, which is suitable for low speed devices. Additionally, the
driver also provide the flexibility of custom ring buffer sizes and
avoid memory allocation for gpadl to offer memory optimization.

Signed-off-by: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>
---
[V2]
- Update driver info in Documentation/driver-api/uio-howto.rst
- Update ring_size sysfs info in Documentation/ABI/stable/sysfs-bus-vmbus
- Remove DRIVER_VERSION
- Remove refcnt
- scnprintf -> sysfs_emit
- sysfs_create_file -> ATTRIBUTE_GROUPS + ".driver.groups";
- sysfs_create_bin_file -> device_create_bin_file
- dev_notice -> dev_err
- remove MODULE_VERSION

 Documentation/ABI/stable/sysfs-bus-vmbus |   7 +
 Documentation/driver-api/uio-howto.rst   |  46 +++++
 drivers/uio/Kconfig                      |  12 ++
 drivers/uio/Makefile                     |   1 +
 drivers/uio/uio_hv_vmbus_client.c        | 217 +++++++++++++++++++++++
 5 files changed, 283 insertions(+)
 create mode 100644 drivers/uio/uio_hv_vmbus_client.c

diff --git a/Documentation/ABI/stable/sysfs-bus-vmbus b/Documentation/ABI/stable/sysfs-bus-vmbus
index 3066feae1d8d..5d075fbd150b 100644
--- a/Documentation/ABI/stable/sysfs-bus-vmbus
+++ b/Documentation/ABI/stable/sysfs-bus-vmbus
@@ -153,6 +153,13 @@ Contact:	Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
 Description:	Binary file created by uio_hv_generic for ring buffer
 Users:		Userspace drivers
 
+What:		/sys/bus/vmbus/devices/<UUID>/ring_size
+Date:		June. 2023
+KernelVersion:	6.4
+Contact:	Saurabh Sengar <ssengar@xxxxxxxxxxxxx>
+Description:	File created by uio_hv_vmbus_client for setting device ring buffer size
+Users:		Userspace drivers
+
 What:           /sys/bus/vmbus/devices/<UUID>/channels/<N>/intr_in_full
 Date:           February 2019
 KernelVersion:  5.0
diff --git a/Documentation/driver-api/uio-howto.rst b/Documentation/driver-api/uio-howto.rst
index 907ffa3b38f5..33b67f876b96 100644
--- a/Documentation/driver-api/uio-howto.rst
+++ b/Documentation/driver-api/uio-howto.rst
@@ -722,6 +722,52 @@ For example::
 
 	/sys/bus/vmbus/devices/3811fe4d-0fa0-4b62-981a-74fc1084c757/channels/21/ring
 
+Generic Hyper-V driver for low speed devices
+============================================
+
+The generic driver is a kernel module named uio_hv_vmbus_client. It
+supports slow devices on the Hyper-V VMBus similar to uio_hv_generic
+for faster devices. This driver also gives flexibility of customized
+ring buffer sizes.
+
+Making the driver recognize the device
+--------------------------------------
+
+Since the driver does not declare any device GUID's, it will not get
+loaded automatically and will not automatically bind to any devices, you
+must load it and allocate id to the driver yourself. For example, to use
+the fcopy device class GUID::
+
+        DEV_UUID=eb765408-105f-49b6-b4aa-c123b64d17d4
+        driverctl -b vmbus set-override $DEV_UUID uio_hv_vmbus_client
+
+You can verify that the device has been bound to the driver by looking
+for it in sysfs, for example like the following::
+
+        ls -l /sys/bus/vmbus/devices/eb765408-105f-49b6-b4aa-c123b64d17d4/driver
+
+Which if successful should print::
+
+      .../eb765408-105f-49b6-b4aa-c123b64d17d4/driver -> ../../../bus/vmbus/drivers/uio_hv_vmbus_client
+
+Things to know about uio_hv_vmbus_client
+----------------------------------------
+
+The uio_hv_vmbus_client driver facilitates the mapping of the Hyper-V device
+ring buffer to userspace and offers an interface to manage it.
+
+The userspace API for mapping and performing read/write operations on the device
+ring buffer is implemented in tools/hv/vmbus_bufring.c. Userspace applications
+can utilize this file as a library to build their logic on top of it.
+
+Additionally, the uio_hv_vmbus_client driver offers a sysfs entry called
+"ring_size" that allows users to adjust the size of the device ring buffer
+before opening it.
+
+For example::
+
+        /sys/bus/vmbus/devices/eb765408-105f-49b6-b4aa-c123b64d17d4/ring_size
+
 Further information
 ===================
 
diff --git a/drivers/uio/Kconfig b/drivers/uio/Kconfig
index 2e16c5338e5b..dcc727e6fd3f 100644
--- a/drivers/uio/Kconfig
+++ b/drivers/uio/Kconfig
@@ -166,6 +166,18 @@ config UIO_HV_GENERIC
 
 	  If you compile this as a module, it will be called uio_hv_generic.
 
+config UIO_HV_SLOW_DEVICES
+	tristate "Generic driver for low speed VMBus devices"
+	depends on HYPERV
+	help
+	  Generic driver that you can bind, dynamically, to any simple
+	  Hyper-V VMBus device with single channel and these devices
+	  uses hypercall instead of monitor bits to interrupt host. This
+	  driver also provide the flexibility of custom ring buffer sizes.
+	  It is useful for slower VMbus devices.
+
+	  If you compile this as a module, it will be called uio_hv_vmbus_client.
+
 config UIO_DFL
 	tristate "Generic driver for DFL (Device Feature List) bus"
 	depends on FPGA_DFL
diff --git a/drivers/uio/Makefile b/drivers/uio/Makefile
index f2f416a14228..44be0f96da34 100644
--- a/drivers/uio/Makefile
+++ b/drivers/uio/Makefile
@@ -11,4 +11,5 @@ obj-$(CONFIG_UIO_PRUSS)         += uio_pruss.o
 obj-$(CONFIG_UIO_MF624)         += uio_mf624.o
 obj-$(CONFIG_UIO_FSL_ELBC_GPCM)	+= uio_fsl_elbc_gpcm.o
 obj-$(CONFIG_UIO_HV_GENERIC)	+= uio_hv_generic.o
+obj-$(CONFIG_UIO_HV_SLOW_DEVICES)	+= uio_hv_vmbus_client.o
 obj-$(CONFIG_UIO_DFL)	+= uio_dfl.o
diff --git a/drivers/uio/uio_hv_vmbus_client.c b/drivers/uio/uio_hv_vmbus_client.c
new file mode 100644
index 000000000000..92fa54271971
--- /dev/null
+++ b/drivers/uio/uio_hv_vmbus_client.c
@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * uio_hv_vmbus_client - UIO driver for low speed VMBus devices
+ *
+ * Copyright (c) 2023, Microsoft Corporation.
+ *
+ * Authors:
+ *   Saurabh Sengar <ssengar@xxxxxxxxxxxxx>
+ *
+ * Since the driver does not declare any device ids, you must allocate
+ * id and bind the device to the driver yourself.  For example:
+ * driverctl -b vmbus set-override <dev uuid> uio_hv_vmbus_client
+ */
+
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/uio_driver.h>
+#include <linux/hyperv.h>
+
+#define DRIVER_AUTHOR	"Saurabh Sengar <ssengar@xxxxxxxxxxxxx>"
+#define DRIVER_DESC	"Generic UIO driver for low speed VMBus devices"
+
+#define DEFAULT_HV_RING_SIZE	VMBUS_RING_SIZE(3 * HV_HYP_PAGE_SIZE)
+static int ring_size = DEFAULT_HV_RING_SIZE;
+
+struct uio_hv_vmbus_dev {
+	struct uio_info info;
+	struct hv_device *device;
+};
+
+/* Sysfs API to allow mmap of the ring buffers */
+static int uio_hv_vmbus_mmap(struct file *filp, struct kobject *kobj,
+			     struct bin_attribute *attr, struct vm_area_struct *vma)
+{
+	struct device *dev = container_of(kobj, struct device, kobj);
+	struct hv_device *hv_dev = container_of(dev, struct hv_device, device);
+	struct vmbus_channel *channel = hv_dev->channel;
+	void *ring_buffer = page_address(channel->ringbuffer_page);
+
+	return vm_iomap_memory(vma, virt_to_phys(ring_buffer),
+			       channel->ringbuffer_pagecount << PAGE_SHIFT);
+}
+
+static const struct bin_attribute ring_buffer_bin_attr = {
+	.attr = {
+		.name = "ringbuffer",
+		.mode = 0600,
+	},
+	.mmap = uio_hv_vmbus_mmap,
+};
+
+/*
+ * This is the irqcontrol callback to be registered to uio_info.
+ * It can be used to disable/enable interrupt from user space processes.
+ *
+ * @param info
+ *  pointer to uio_info.
+ * @param irq_state
+ *  state value. 1 to enable interrupt, 0 to disable interrupt.
+ */
+static int uio_hv_vmbus_irqcontrol(struct uio_info *info, s32 irq_state)
+{
+	struct uio_hv_vmbus_dev *pdata = info->priv;
+	struct hv_device *hv_dev = pdata->device;
+
+	/* Issue a full memory barrier before triggering the notification */
+	virt_mb();
+
+	vmbus_setevent(hv_dev->channel);
+	return 0;
+}
+
+/*
+ * Callback from vmbus_event when something is in inbound ring.
+ */
+static void uio_hv_vmbus_channel_cb(void *context)
+{
+	struct uio_hv_vmbus_dev *pdata = context;
+
+	/* Issue a full memory barrier before sending the event to userspace */
+	virt_mb();
+
+	uio_event_notify(&pdata->info);
+}
+
+static int uio_hv_vmbus_open(struct uio_info *info, struct inode *inode)
+{
+	struct uio_hv_vmbus_dev *pdata = container_of(info, struct uio_hv_vmbus_dev, info);
+	struct hv_device *hv_dev = pdata->device;
+	struct vmbus_channel *channel = hv_dev->channel;
+	int ret;
+
+	ret = vmbus_open(channel, ring_size, ring_size, NULL, 0,
+			 uio_hv_vmbus_channel_cb, pdata);
+	if (ret) {
+		dev_err(&hv_dev->device, "error %d when opening the channel\n", ret);
+		return ret;
+	}
+	channel->inbound.ring_buffer->interrupt_mask = 0;
+	set_channel_read_mode(channel, HV_CALL_ISR);
+
+	ret = device_create_bin_file(&hv_dev->device, &ring_buffer_bin_attr);
+	if (ret)
+		dev_err(&hv_dev->device, "sysfs create ring bin file failed; %d\n", ret);
+
+	return ret;
+}
+
+/* VMbus primary channel is closed on last close */
+static int uio_hv_vmbus_release(struct uio_info *info, struct inode *inode)
+{
+	struct uio_hv_vmbus_dev *pdata = container_of(info, struct uio_hv_vmbus_dev, info);
+	struct hv_device *hv_dev = pdata->device;
+	struct vmbus_channel *channel = hv_dev->channel;
+
+	device_remove_bin_file(&hv_dev->device, &ring_buffer_bin_attr);
+	vmbus_close(channel);
+
+	return 0;
+}
+
+static ssize_t ring_size_show(struct device *dev, struct device_attribute *attr,
+			      char *buf)
+{
+	return sysfs_emit(buf, "%d\n", ring_size);
+}
+
+static ssize_t ring_size_store(struct device *dev, struct device_attribute *attr,
+			       const char *buf, size_t count)
+{
+	unsigned int val;
+
+	if (kstrtouint(buf, 0, &val) < 0)
+		return -EINVAL;
+
+	if (val < HV_HYP_PAGE_SIZE)
+		return -EINVAL;
+
+	ring_size = val;
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(ring_size);
+
+static struct attribute *uio_hv_vmbus_client_attrs[] = {
+	&dev_attr_ring_size.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(uio_hv_vmbus_client);
+
+static int uio_hv_vmbus_probe(struct hv_device *dev, const struct hv_vmbus_device_id *dev_id)
+{
+	struct uio_hv_vmbus_dev *pdata;
+	int ret;
+	char *name = NULL;
+
+	pdata = devm_kzalloc(&dev->device, sizeof(*pdata), GFP_KERNEL);
+	if (!pdata)
+		return -ENOMEM;
+
+	name = kasprintf(GFP_KERNEL, "%pUl", &dev->dev_instance);
+
+	/* Fill general uio info */
+	pdata->info.name = name; /* /sys/class/uio/uioX/name */
+	pdata->info.version = "1";
+	pdata->info.irqcontrol = uio_hv_vmbus_irqcontrol;
+	pdata->info.open = uio_hv_vmbus_open;
+	pdata->info.release = uio_hv_vmbus_release;
+	pdata->info.irq = UIO_IRQ_CUSTOM;
+	pdata->info.priv = pdata;
+	pdata->device = dev;
+
+	ret = uio_register_device(&dev->device, &pdata->info);
+	if (ret) {
+		dev_err(&dev->device, "uio_hv_vmbus register failed\n");
+		return ret;
+	}
+
+	hv_set_drvdata(dev, pdata);
+
+	return 0;
+}
+
+static void uio_hv_vmbus_remove(struct hv_device *dev)
+{
+	struct uio_hv_vmbus_dev *pdata = hv_get_drvdata(dev);
+
+	if (pdata)
+		uio_unregister_device(&pdata->info);
+}
+
+static struct hv_driver uio_hv_vmbus_drv = {
+	.driver.dev_groups = uio_hv_vmbus_client_groups,
+	.name = "uio_hv_vmbus_client",
+	.id_table = NULL, /* only dynamic id's */
+	.probe = uio_hv_vmbus_probe,
+	.remove = uio_hv_vmbus_remove,
+};
+
+static int __init uio_hv_vmbus_init(void)
+{
+	return vmbus_driver_register(&uio_hv_vmbus_drv);
+}
+
+static void __exit uio_hv_vmbus_exit(void)
+{
+	vmbus_driver_unregister(&uio_hv_vmbus_drv);
+}
+
+module_init(uio_hv_vmbus_init);
+module_exit(uio_hv_vmbus_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR(DRIVER_AUTHOR);
+MODULE_DESCRIPTION(DRIVER_DESC);
-- 
2.34.1