Re: [PATCH v3] i2c: virtio: add a virtio i2c frontend driver

From: Andy Shevchenko
Date: Tue Sep 22 2020 - 07:26:12 EST

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On Tue, Sep 22, 2020 at 10:58:43AM +0800, Jie Deng wrote:
> 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>
> ---
> The device ID request:
> https://github.com/oasis-tcs/virtio-spec/issues/85
>
> The specification:
> https://lists.oasis-open.org/archives/virtio-comment/202009/msg00021.html
>
> Changes in v3:
> - Move the interface into uAPI according to Jason.
> - Fix issues reported by Dan Carpenter.
> - Fix typo reported by Randy.
>
> Changes in v2:
> - Addressed comments received from Michael, Andy and Jason.
>
> drivers/i2c/busses/Kconfig | 11 ++
> drivers/i2c/busses/Makefile | 3 +
> drivers/i2c/busses/i2c-virtio.c | 256 ++++++++++++++++++++++++++++++++++++++++
> include/uapi/linux/virtio_i2c.h | 31 +++++
> include/uapi/linux/virtio_ids.h | 1 +
> 5 files changed, 302 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 293e7a0..f2f6543 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..48fd780
> --- /dev/null
> +++ b/drivers/i2c/busses/i2c-virtio.c
> @@ -0,0 +1,256 @@
> +// 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_i2c.h>
> +
> +/**
> + * 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;
> + u8 *buf;
> + u8 status;
> +};
> +
> +/**
> + * struct virtio_i2c - virtio I2C data
> + * @vdev: virtio device for this controller
> + * @completion: completion of virtio I2C message
> + * @vmsg: the virtio I2C message for communication
> + * @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 virtio_i2c_msg vmsg;
> + 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 = cpu_to_le16(msg->addr);
> + vmsg->hdr.flags = cpu_to_le16(msg->flags);
> + vmsg->hdr.len = cpu_to_le16(msg->len);
> +
> + vmsg->buf = kzalloc(msg->len, GFP_KERNEL);
> + if (!vmsg->buf)
> + return -ENOMEM;
> +
> + sg_init_one(&hdr, &vmsg->hdr, sizeof(struct virtio_i2c_hdr));
> + sgs[outcnt++] = &hdr;
> + if (msg->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 virtqueue *vq = vi->vq;
> + struct virtio_i2c_msg *vmsg;
> + unsigned long time_left;
> + int len, i, ret = 0;
> +
> + mutex_lock(&vi->i2c_lock);
> + vmsg = &vi->vmsg;
> + vmsg->buf = NULL;
> +
> + for (i = 0; i < num; i++) {
> + ret = virtio_i2c_add_msg(vq, vmsg, &msgs[i]);
> + if (ret) {
> + dev_err(&adap->dev, "failed to add msg[%d] to virtqueue.\n", i);
> + break;
> + }
> +
> + 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);
> + break;
> + }
> +
> + vmsg = (struct virtio_i2c_msg *)virtqueue_get_buf(vq, &len);
> + /* vmsg should point to the same address with &vi->vmsg */

> + if ((!vmsg) || (vmsg != &vi->vmsg)) {

This is a bit difficult to read (esp. taking into account the above comment)
besides the fact of redundant parentheses. Why not simply:

if (!(vmsg && vmsg == &vi->vmsg)) {

?

> + dev_err(&adap->dev, "msg[%d]: addr=0x%x virtqueue error.\n",
> + i, msgs[i].addr);
> + break;
> + }
> +
> + if (vmsg->status != VIRTIO_I2C_MSG_OK) {
> + dev_err(&adap->dev, "msg[%d]: addr=0x%x error=%d.\n",
> + i, msgs[i].addr, vmsg->status);
> + break;
> + }
> +
> + if ((msgs[i].flags & I2C_M_RD) && msgs[i].len)
> + memcpy(msgs[i].buf, vmsg->buf, msgs[i].len);
> +
> + kfree(vmsg->buf);
> + vmsg->buf = NULL;
> +
> + reinit_completion(&vi->completion);
> + }
> +
> + mutex_unlock(&vi->i2c_lock);
> + kfree(vi->vmsg.buf);
> + vi->vmsg.buf = NULL;
> + return ((ret < 0) ? ret : i);
> +}
> +
> +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 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) {
> + 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_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_i2c.h b/include/uapi/linux/virtio_i2c.h
> new file mode 100644
> index 0000000..7413e45
> --- /dev/null
> +++ b/include/uapi/linux/virtio_i2c.h
> @@ -0,0 +1,31 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later OR BSD-3-Clause */
> +/*
> + * Definitions for virtio I2C Adpter
> + *
> + * Copyright (c) 2020 Intel Corporation. All rights reserved.
> + */
> +
> +#ifndef _UAPI_LINUX_VIRTIO_I2C_H
> +#define _UAPI_LINUX_VIRTIO_I2C_H
> +
> +#include <linux/types.h>
> +#include <linux/virtio_ids.h>
> +#include <linux/virtio_config.h>
> +
> +/**
> + * 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 {
> + __le16 addr;
> + __le16 flags;
> + __le16 len;
> +};
> +
> +/* 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 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
>

--
With Best Regards,
Andy Shevchenko

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