[PATCH] i2c: virtio: add a virtio i2c frontend driver

[Jie Deng]

Add an I2C bus driver for virtio para-virtualization.

The controller can be emulated by the backend driver in
any device model software by following the virtio protocol.

This driver communicates with the backend driver through a
virtio I2C message structure which includes following parts:

- Header: i2c_msg addr, flags, len.
- Data buffer: the pointer to the i2c msg data.
- Status: the processing result from the backend.

People may implement different backend drivers to emulate
different controllers according to their needs. A backend
example can be found in the device model of the open source
project ACRN. For more information, please refer to
https://projectacrn.org.

The virtio device ID 34 is used for this I2C adpter since IDs
before 34 have been reserved by other virtio devices.

Co-developed-by: Conghui Chen <conghui.chen@xxxxxxxxx>
Signed-off-by: Conghui Chen <conghui.chen@xxxxxxxxx>
Signed-off-by: Jie Deng <jie.deng@xxxxxxxxx>
Reviewed-by: Shuo Liu <shuo.a.liu@xxxxxxxxx>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
---
 drivers/i2c/busses/Kconfig      |  11 ++
 drivers/i2c/busses/Makefile     |   3 +
 drivers/i2c/busses/i2c-virtio.c | 276 ++++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/virtio_ids.h |   1 +
 4 files changed, 291 insertions(+)
 create mode 100644 drivers/i2c/busses/i2c-virtio.c

diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index 293e7a0..70c8e30 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -21,6 +21,17 @@ config I2C_ALI1535
 	  This driver can also be built as a module.  If so, the module
 	  will be called i2c-ali1535.
 
+config I2C_VIRTIO
+	tristate "Virtio I2C Adapter"
+	depends on VIRTIO
+	help
+	  If you say yes to this option, support will be included for the virtio
+	  i2c adapter driver. The hardware can be emulated by any device model
+	  software according to the virtio protocol.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called i2c-virtio.
+
 config I2C_ALI1563
 	tristate "ALI 1563"
 	depends on PCI
diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
index 19aff0e..821acfa 100644
--- a/drivers/i2c/busses/Makefile
+++ b/drivers/i2c/busses/Makefile
@@ -6,6 +6,9 @@
 # ACPI drivers
 obj-$(CONFIG_I2C_SCMI)		+= i2c-scmi.o
 
+# VIRTIO I2C host controller driver
+obj-$(CONFIG_I2C_VIRTIO)	+= i2c-virtio.o
+
 # PC SMBus host controller drivers
 obj-$(CONFIG_I2C_ALI1535)	+= i2c-ali1535.o
 obj-$(CONFIG_I2C_ALI1563)	+= i2c-ali1563.o
diff --git a/drivers/i2c/busses/i2c-virtio.c b/drivers/i2c/busses/i2c-virtio.c
new file mode 100644
index 0000000..47f9fd1
--- /dev/null
+++ b/drivers/i2c/busses/i2c-virtio.c
@@ -0,0 +1,276 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Virtio I2C Bus Driver
+ *
+ * Copyright (c) 2020 Intel Corporation. All rights reserved.
+ */
+
+#include <linux/acpi.h>
+#include <linux/completion.h>
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/io.h>
+#include <linux/jiffies.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/wait.h>
+
+#include <linux/virtio.h>
+#include <linux/virtio_ids.h>
+#include <linux/virtio_config.h>
+
+#define VIRTIO_I2C_MSG_OK	0
+#define VIRTIO_I2C_MSG_ERR	1
+
+/**
+ * struct virtio_i2c_hdr - the virtio I2C message header structure
+ * @addr: i2c_msg addr, the slave address
+ * @flags: i2c_msg flags
+ * @len: i2c_msg len
+ */
+struct virtio_i2c_hdr {
+	__virtio16 addr;
+	__virtio16 flags;
+	__virtio16 len;
+} __packed;
+
+/**
+ * struct virtio_i2c_msg - the virtio I2C message structure
+ * @hdr: the virtio I2C message header
+ * @buf: virtio I2C message data buffer
+ * @status: the processing result from the backend
+ */
+struct virtio_i2c_msg {
+	struct virtio_i2c_hdr hdr;
+	char *buf;
+	u8 status;
+};
+
+/**
+ * struct virtio_i2c - virtio I2C data
+ * @vdev: virtio device for this controller
+ * @completion: completion of virtio I2C message
+ * @adap: I2C adapter for this controller
+ * @i2c_lock: lock for virtqueue processing
+ * @vq: the virtio virtqueue for communication
+ */
+struct virtio_i2c {
+	struct virtio_device *vdev;
+	struct completion completion;
+	struct i2c_adapter adap;
+	struct mutex i2c_lock;
+	struct virtqueue *vq;
+};
+
+static void virtio_i2c_msg_done(struct virtqueue *vq)
+{
+	struct virtio_i2c *vi = vq->vdev->priv;
+
+	complete(&vi->completion);
+}
+
+static int virtio_i2c_add_msg(struct virtqueue *vq,
+			      struct virtio_i2c_msg *vmsg,
+			      struct i2c_msg *msg)
+{
+	struct scatterlist *sgs[3], hdr, bout, bin, status;
+	int outcnt = 0, incnt = 0;
+
+	if (!msg->len)
+		return -EINVAL;
+
+	vmsg->hdr.addr = msg->addr;
+	vmsg->hdr.flags = msg->flags;
+	vmsg->hdr.len = msg->len;
+
+	vmsg->buf = kzalloc(vmsg->hdr.len, GFP_KERNEL);
+	if (!vmsg->buf)
+		return -ENOMEM;
+
+	sg_init_one(&hdr, &vmsg->hdr, sizeof(struct virtio_i2c_hdr));
+	sgs[outcnt++] = &hdr;
+	if (vmsg->hdr.flags & I2C_M_RD) {
+		sg_init_one(&bin, vmsg->buf, msg->len);
+		sgs[outcnt + incnt++] = &bin;
+	} else {
+		memcpy(vmsg->buf, msg->buf, msg->len);
+		sg_init_one(&bout, vmsg->buf, msg->len);
+		sgs[outcnt++] = &bout;
+	}
+	sg_init_one(&status, &vmsg->status, sizeof(vmsg->status));
+	sgs[outcnt + incnt++] = &status;
+
+	return virtqueue_add_sgs(vq, sgs, outcnt, incnt, vmsg, GFP_KERNEL);
+}
+
+static int virtio_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
+{
+	struct virtio_i2c *vi = i2c_get_adapdata(adap);
+	struct virtio_i2c_msg *vmsg_o, *vmsg_i;
+	struct virtqueue *vq = vi->vq;
+	unsigned long time_left;
+	int len, i, ret = 0;
+
+	vmsg_o = kzalloc(sizeof(*vmsg_o), GFP_KERNEL);
+	if (!vmsg_o)
+		return -ENOMEM;
+
+	mutex_lock(&vi->i2c_lock);
+	vmsg_o->buf = NULL;
+	for (i = 0; i < num; i++) {
+		ret = virtio_i2c_add_msg(vq, vmsg_o, &msgs[i]);
+		if (ret) {
+			dev_err(&adap->dev, "failed to add msg[%d] to virtqueue.\n", i);
+			goto err_unlock_free;
+		}
+
+		virtqueue_kick(vq);
+
+		time_left = wait_for_completion_timeout(&vi->completion, adap->timeout);
+		if (!time_left) {
+			dev_err(&adap->dev, "msg[%d]: addr=0x%x timeout.\n", i, msgs[i].addr);
+			ret = i;
+			goto err_unlock_free;
+		}
+
+		vmsg_i = (struct virtio_i2c_msg *)virtqueue_get_buf(vq, &len);
+		if (vmsg_i) {
+			/* vmsg_i should point to the same address with vmsg_o */
+			if (vmsg_i != vmsg_o) {
+				dev_err(&adap->dev, "msg[%d]: addr=0x%x virtqueue error.\n",
+					i, vmsg_i->hdr.addr);
+				ret = i;
+				goto err_unlock_free;
+			}
+			if (vmsg_i->status != VIRTIO_I2C_MSG_OK) {
+				dev_err(&adap->dev, "msg[%d]: addr=0x%x error=%d.\n",
+					i, vmsg_i->hdr.addr, vmsg_i->status);
+				ret = i;
+				goto err_unlock_free;
+			}
+			if ((vmsg_i->hdr.flags & I2C_M_RD) && vmsg_i->hdr.len)
+				memcpy(msgs[i].buf, vmsg_i->buf, vmsg_i->hdr.len);
+
+			kfree(vmsg_i->buf);
+			vmsg_i->buf = NULL;
+		}
+		reinit_completion(&vi->completion);
+	}
+	if (i == num)
+		ret = num;
+
+err_unlock_free:
+	mutex_unlock(&vi->i2c_lock);
+	kfree(vmsg_o->buf);
+	kfree(vmsg_o);
+	return ret;
+}
+
+static void virtio_i2c_del_vqs(struct virtio_device *vdev)
+{
+	vdev->config->reset(vdev);
+	vdev->config->del_vqs(vdev);
+}
+
+static int virtio_i2c_setup_vqs(struct virtio_i2c *vi)
+{
+	struct virtio_device *vdev = vi->vdev;
+
+	vi->vq = virtio_find_single_vq(vdev, virtio_i2c_msg_done, "i2c-msg");
+	return PTR_ERR_OR_ZERO(vi->vq);
+}
+
+static u32 virtio_i2c_func(struct i2c_adapter *adap)
+{
+	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
+}
+
+static struct i2c_algorithm virtio_algorithm = {
+	.master_xfer = virtio_i2c_xfer,
+	.functionality = virtio_i2c_func,
+};
+
+static struct i2c_adapter virtio_adapter = {
+	.owner = THIS_MODULE,
+	.name = "Virtio I2C Adapter",
+	.class = I2C_CLASS_DEPRECATED,
+	.algo = &virtio_algorithm,
+};
+
+static int virtio_i2c_probe(struct virtio_device *vdev)
+{
+	struct device *pdev = vdev->dev.parent;
+	struct virtio_i2c *vi;
+	int ret;
+
+	vi = devm_kzalloc(&vdev->dev, sizeof(*vi), GFP_KERNEL);
+	if (!vi)
+		return -ENOMEM;
+
+	vdev->priv = vi;
+	vi->vdev = vdev;
+
+	mutex_init(&vi->i2c_lock);
+	init_completion(&vi->completion);
+
+	ret = virtio_i2c_setup_vqs(vi);
+	if (ret)
+		return ret;
+
+	vi->adap = virtio_adapter;
+	i2c_set_adapdata(&vi->adap, vi);
+	vi->adap.dev.parent = &vdev->dev;
+	/* Setup ACPI node for slave devices which will be probed through ACPI */
+	ACPI_COMPANION_SET(&vi->adap.dev, ACPI_COMPANION(pdev));
+	vi->adap.timeout = HZ / 10;
+	ret = i2c_add_adapter(&vi->adap);
+	if (ret) {
+		dev_err(&vdev->dev, "failed to add virtio-i2c adapter.\n");
+		virtio_i2c_del_vqs(vdev);
+	}
+
+	return ret;
+}
+
+static void virtio_i2c_remove(struct virtio_device *vdev)
+{
+	struct virtio_i2c *vi = vdev->priv;
+
+	i2c_del_adapter(&vi->adap);
+	virtio_i2c_del_vqs(vdev);
+}
+
+static struct virtio_device_id id_table[] = {
+	{ VIRTIO_ID_I2C_ADPTER, VIRTIO_DEV_ANY_ID },
+	{}
+};
+MODULE_DEVICE_TABLE(virtio, id_table);
+
+static int __maybe_unused virtio_i2c_freeze(struct virtio_device *vdev)
+{
+	virtio_i2c_del_vqs(vdev);
+	return 0;
+}
+
+static int __maybe_unused virtio_i2c_restore(struct virtio_device *vdev)
+{
+	return virtio_i2c_setup_vqs(vdev->priv);
+}
+
+static struct virtio_driver virtio_i2c_driver = {
+	.id_table	= id_table,
+	.probe		= virtio_i2c_probe,
+	.remove		= virtio_i2c_remove,
+	.driver	= {
+		.name	= "i2c_virtio",
+	},
+#ifdef CONFIG_PM_SLEEP
+	.freeze = virtio_i2c_freeze,
+	.restore = virtio_i2c_restore,
+#endif
+};
+module_virtio_driver(virtio_i2c_driver);
+
+MODULE_DESCRIPTION("Virtio i2c bus driver");
+MODULE_LICENSE("GPL");
diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
index b052355..398ef2d 100644
--- a/include/uapi/linux/virtio_ids.h
+++ b/include/uapi/linux/virtio_ids.h
@@ -48,5 +48,6 @@
 #define VIRTIO_ID_FS           26 /* virtio filesystem */
 #define VIRTIO_ID_PMEM         27 /* virtio pmem */
 #define VIRTIO_ID_MAC80211_HWSIM 29 /* virtio mac80211-hwsim */
+#define VIRTIO_ID_I2C_ADPTER   34 /* virtio i2c adpter */
 
 #endif /* _LINUX_VIRTIO_IDS_H */
-- 
2.7.4