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    Subject[PATCH v11] i2c: virtio: add a virtio i2c frontend driver
    Date
    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 v10 -> v11
    - Remove vi->adap.class = I2C_CLASS_DEPRECATED.
    - Use #ifdef CONFIG_PM_SLEEP to replace the "__maybe_unused".
    - Remove "struct mutex lock" in "struct virtio_i2c".
    - Support zero-length request.
    - Remove unnecessary logs.
    - Remove vi->adap.timeout = HZ / 10, just use the default value.
    - Use BIT(0) to define VIRTIO_I2C_FLAGS_FAIL_NEXT.
    - Add the virtio_device index to adapter's naming mechanism.

    drivers/i2c/busses/Kconfig | 11 ++
    drivers/i2c/busses/Makefile | 3 +
    drivers/i2c/busses/i2c-virtio.c | 265 ++++++++++++++++++++++++++++++++++++++++
    include/uapi/linux/virtio_i2c.h | 41 +++++++
    include/uapi/linux/virtio_ids.h | 1 +
    5 files changed, 321 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 10acece..e47616a 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 69e9963..9843756 100644
    --- a/drivers/i2c/busses/Makefile
    +++ b/drivers/i2c/busses/Makefile
    @@ -147,4 +147,7 @@ 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..97dda54
    --- /dev/null
    +++ b/drivers/i2c/busses/i2c-virtio.c
    @@ -0,0 +1,265 @@
    +// 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
    + * @vq: the virtio virtqueue for communication
    + */
    +struct virtio_i2c {
    + struct virtio_device *vdev;
    + struct completion completion;
    + struct i2c_adapter adap;
    + 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++) {
    + /*
    + * 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) {
    + 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;
    +
    + ret = virtio_i2c_send_reqs(vq, reqs, msgs, num);
    + if (ret == 0)
    + goto err_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_free:
    + 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;
    +
    + 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),
    + "i2c_virtio at virtio bus %d", vdev->index);
    + vi->adap.algo = &virtio_algorithm;
    + vi->adap.dev.parent = &vdev->dev;
    + 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);
    +
    + 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);
    +
    +#ifdef CONFIG_PM_SLEEP
    +static int virtio_i2c_freeze(struct virtio_device *vdev)
    +{
    + virtio_i2c_del_vqs(vdev);
    + return 0;
    +}
    +
    +static int virtio_i2c_restore(struct virtio_device *vdev)
    +{
    + return virtio_i2c_setup_vqs(vdev->priv);
    +}
    +#endif
    +
    +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..3cc1609
    --- /dev/null
    +++ b/include/uapi/linux/virtio_i2c.h
    @@ -0,0 +1,41 @@
    +/* 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>
    +#include <linux/bits.h>
    +
    +/* The bit 0 of the @virtio_i2c_out_hdr.@flags, used to group the requests */
    +#define VIRTIO_I2C_FLAGS_FAIL_NEXT BIT(0)
    +
    +/**
    + * 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 4fe842c..3b5f05a 100644
    --- a/include/uapi/linux/virtio_ids.h
    +++ b/include/uapi/linux/virtio_ids.h
    @@ -55,6 +55,7 @@
    #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 */
    #define VIRTIO_ID_BT 40 /* virtio bluetooth */

    #endif /* _LINUX_VIRTIO_IDS_H */
    --
    2.7.4
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