[PATCH v10] i2c: virtio: add a virtio i2c frontend driver

Jie Deng
2021-03-23T06:20:25Z

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.

The device specification can be found on
https://lists.oasis-open.org/archives/virtio-comment/202101/msg00008.html.

By following the specification, people may implement different
backend drivers to emulate different controllers according to
their needs.

Co-developed-by: Conghui Chen <conghui.chen@intel.com>
Signed-off-by: Conghui Chen <conghui.chen@intel.com>
Signed-off-by: Jie Deng <jie.deng@intel.com>
---
Changes in v10:
- Fix some typo errors.
- Refined the virtio_i2c_complete_reqs to use less code lines.

Changes in v9:
- Remove the virtio_adapter and update its members in probe.
- Refined the virtio_i2c_complete_reqs for buf free.

Changes in v8:
- Make virtio_i2c.adap a pointer.
- Mark members in virtio_i2c_req with ____cacheline_aligned.

Changes in v7:
- Remove unused headers.
- Update Makefile and Kconfig.
- Add the cleanup after completing reqs.
- Avoid memcpy for data marked with I2C_M_DMA_SAFE.
- Fix something reported by kernel test robot.

Changes in v6:
- Move struct virtio_i2c_req into the driver.
- Use only one buf in struct virtio_i2c_req.

Changes in v5:
- The first version based on the acked specification.

drivers/i2c/busses/Kconfig | 11 ++
drivers/i2c/busses/Makefile | 3 +
drivers/i2c/busses/i2c-virtio.c | 276 ++++++++++++++++++++++++++++++++++++++++
include/uapi/linux/virtio_i2c.h | 40 ++++++
include/uapi/linux/virtio_ids.h | 1 +
5 files changed, 331 insertions(+)
create mode 100644 drivers/i2c/busses/i2c-virtio.c
create mode 100644 include/uapi/linux/virtio_i2c.h

diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index 05ebf75..cb8d0d8 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"
+ select 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 615f35e..efdd3f3 100644
--- a/drivers/i2c/busses/Makefile
+++ b/drivers/i2c/busses/Makefile
@@ -145,4 +145,7 @@ obj-$(CONFIG_I2C_XGENE_SLIMPRO) += i2c-xgene-slimpro.o
obj-$(CONFIG_SCx200_ACB) += scx200_acb.o
obj-$(CONFIG_I2C_FSI) += i2c-fsi.o

+# VIRTIO I2C host controller driver
+obj-$(CONFIG_I2C_VIRTIO) += i2c-virtio.o
+
ccflags-$(CONFIG_I2C_DEBUG_BUS) := -DDEBUG
diff --git a/drivers/i2c/busses/i2c-virtio.c b/drivers/i2c/busses/i2c-virtio.c
new file mode 100644
index 0000000..99a1e30
--- /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
+ *
+ * The Virtio I2C Specification:
+ * https://raw.githubusercontent.com/oasis-tcs/virtio-spec/master/virtio-i2c.tex
+ *
+ * Copyright (c) 2021 Intel Corporation. All rights reserved.
+ */
+
+#include <linux/acpi.h>
+#include <linux/completion.h>
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/virtio.h>
+#include <linux/virtio_ids.h>
+#include <linux/virtio_config.h>
+#include <linux/virtio_i2c.h>
+
+/**
+ * struct virtio_i2c - virtio I2C data
+ * @vdev: virtio device for this controller
+ * @completion: completion of virtio I2C message
+ * @adap: I2C adapter for this controller
+ * @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 lock;
+ struct virtqueue *vq;
+};
+
+/**
+ * struct virtio_i2c_req - the virtio I2C request structure
+ * @out_hdr: the OUT header of the virtio I2C message
+ * @buf: the buffer into which data is read, or from which it's written
+ * @in_hdr: the IN header of the virtio I2C message
+ */
+struct virtio_i2c_req {
+ struct virtio_i2c_out_hdr out_hdr ____cacheline_aligned;
+ uint8_t *buf ____cacheline_aligned;
+ struct virtio_i2c_in_hdr in_hdr ____cacheline_aligned;
+};
+
+static void virtio_i2c_msg_done(struct virtqueue *vq)
+{
+ struct virtio_i2c *vi = vq->vdev->priv;
+
+ complete(&vi->completion);
+}
+
+static int virtio_i2c_send_reqs(struct virtqueue *vq,
+ struct virtio_i2c_req *reqs,
+ struct i2c_msg *msgs, int nr)
+{
+ struct scatterlist *sgs[3], out_hdr, msg_buf, in_hdr;
+ int i, outcnt, incnt, err = 0;
+
+ for (i = 0; i < nr; i++) {
+ if (!msgs[i].len)
+ break;
+
+ /*
+ * Only 7-bit mode supported for this moment. For the address format,
+ * Please check the Virtio I2C Specification.
+ */
+ reqs[i].out_hdr.addr = cpu_to_le16(msgs[i].addr << 1);
+
+ if (i != nr - 1)
+ reqs[i].out_hdr.flags = cpu_to_le32(VIRTIO_I2C_FLAGS_FAIL_NEXT);
+
+ outcnt = incnt = 0;
+ sg_init_one(&out_hdr, &reqs[i].out_hdr, sizeof(reqs[i].out_hdr));
+ sgs[outcnt++] = &out_hdr;
+
+ reqs[i].buf = i2c_get_dma_safe_msg_buf(&msgs[i], 1);
+ if (!reqs[i].buf)
+ break;
+
+ sg_init_one(&msg_buf, reqs[i].buf, msgs[i].len);
+
+ if (msgs[i].flags & I2C_M_RD)
+ sgs[outcnt + incnt++] = &msg_buf;
+ else
+ sgs[outcnt++] = &msg_buf;
+
+ sg_init_one(&in_hdr, &reqs[i].in_hdr, sizeof(reqs[i].in_hdr));
+ sgs[outcnt + incnt++] = &in_hdr;
+
+ err = virtqueue_add_sgs(vq, sgs, outcnt, incnt, &reqs[i], GFP_KERNEL);
+ if (err < 0) {
+ pr_err("failed to add msg[%d] to virtqueue.\n", i);
+ i2c_put_dma_safe_msg_buf(reqs[i].buf, &msgs[i], false);
+ break;
+ }
+ }
+
+ return i;
+}
+
+static int virtio_i2c_complete_reqs(struct virtqueue *vq,
+ struct virtio_i2c_req *reqs,
+ struct i2c_msg *msgs, int nr,
+ bool timeout)
+{
+ struct virtio_i2c_req *req;
+ bool failed = timeout;
+ unsigned int len;
+ int i, j = 0;
+
+ for (i = 0; i < nr; i++) {
+ /* Detach the ith request from the vq */
+ req = virtqueue_get_buf(vq, &len);
+
+ /*
+ * Condition (req && req == &reqs[i]) should always meet since
+ * we have total nr requests in the vq.
+ */
+ if (!failed && (WARN_ON(!(req && req == &reqs[i])) ||
+ (req->in_hdr.status != VIRTIO_I2C_MSG_OK)))
+ failed = true;
+
+ i2c_put_dma_safe_msg_buf(reqs[i].buf, &msgs[i], !failed);
+ if (!failed)
+ ++j;
+ }
+
+ return (timeout ? -ETIMEDOUT : j);
+}
+
+static int virtio_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
+{
+ struct virtio_i2c *vi = i2c_get_adapdata(adap);
+ struct virtqueue *vq = vi->vq;
+ struct virtio_i2c_req *reqs;
+ unsigned long time_left;
+ int ret, nr;
+
+ reqs = kcalloc(num, sizeof(*reqs), GFP_KERNEL);
+ if (!reqs)
+ return -ENOMEM;
+
+ mutex_lock(&vi->lock);
+
+ ret = virtio_i2c_send_reqs(vq, reqs, msgs, num);
+ if (ret == 0)
+ goto err_unlock_free;
+
+ nr = ret;
+ reinit_completion(&vi->completion);
+ virtqueue_kick(vq);
+
+ time_left = wait_for_completion_timeout(&vi->completion, adap->timeout);
+ if (!time_left)
+ dev_err(&adap->dev, "virtio i2c backend timeout.\n");
+
+ ret = virtio_i2c_complete_reqs(vq, reqs, msgs, nr, !time_left);
+
+err_unlock_free:
+ mutex_unlock(&vi->lock);
+ kfree(reqs);
+ 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, "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 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->lock);
+ init_completion(&vi->completion);
+
+ ret = virtio_i2c_setup_vqs(vi);
+ if (ret)
+ return ret;
+
+ vi->adap.owner = THIS_MODULE;
+ snprintf(vi->adap.name, sizeof(vi->adap.name), "Virtio I2C Adapter");
+ vi->adap.class = I2C_CLASS_DEPRECATED;
+ vi->adap.algo = &virtio_algorithm;
+ vi->adap.dev.parent = &vdev->dev;
+ vi->adap.timeout = HZ / 10;
+ i2c_set_adapdata(&vi->adap, vi);
+
+ /* Setup ACPI node for controlled devices which will be probed through ACPI */
+ ACPI_COMPANION_SET(&vi->adap.dev, ACPI_COMPANION(pdev));
+
+ ret = i2c_add_adapter(&vi->adap);
+ if (ret) {
+ virtio_i2c_del_vqs(vdev);
+ dev_err(&vdev->dev, "failed to add virtio-i2c adapter.\n");
+ }
+
+ 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_ADAPTER, 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_AUTHOR("Jie Deng <jie.deng@intel.com>");
+MODULE_AUTHOR("Conghui Chen <conghui.chen@intel.com>");
+MODULE_DESCRIPTION("Virtio i2c bus driver");
+MODULE_LICENSE("GPL");
diff --git a/include/uapi/linux/virtio_i2c.h b/include/uapi/linux/virtio_i2c.h
new file mode 100644
index 0000000..bbcfb2c
--- /dev/null
+++ b/include/uapi/linux/virtio_i2c.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later WITH Linux-syscall-note */
+/*
+ * Definitions for virtio I2C Adpter
+ *
+ * Copyright (c) 2021 Intel Corporation. All rights reserved.
+ */
+
+#ifndef _UAPI_LINUX_VIRTIO_I2C_H
+#define _UAPI_LINUX_VIRTIO_I2C_H
+
+#include <linux/types.h>
+
+/* The bit 0 of the @virtio_i2c_out_hdr.@flags, used to group the requests */
+#define VIRTIO_I2C_FLAGS_FAIL_NEXT 0x00000001
+
+/**
+ * struct virtio_i2c_out_hdr - the virtio I2C message OUT header
+ * @addr: the controlled device address
+ * @padding: used to pad to full dword
+ * @flags: used for feature extensibility
+ */
+struct virtio_i2c_out_hdr {
+ __le16 addr;
+ __le16 padding;
+ __le32 flags;
+};
+
+/**
+ * struct virtio_i2c_in_hdr - the virtio I2C message IN header
+ * @status: the processing result from the backend
+ */
+struct virtio_i2c_in_hdr {
+ __u8 status;
+};
+
+/* The final status written by the device */
+#define VIRTIO_I2C_MSG_OK 0
+#define VIRTIO_I2C_MSG_ERR 1
+
+#endif /* _UAPI_LINUX_VIRTIO_I2C_H */
diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
index bc1c062..b89391d 100644
--- a/include/uapi/linux/virtio_ids.h
+++ b/include/uapi/linux/virtio_ids.h
@@ -54,5 +54,6 @@
#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_ADAPTER 34 /* virtio i2c adapter */

#endif /* _LINUX_VIRTIO_IDS_H */
--
2.7.4