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Subject: Re: [PATCH v6] i2c: virtio: add a virtio i2c frontend driver
To:     Jie Deng <jie.deng@intel.com>, linux-i2c@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
Cc:     mst@redhat.com, wsa@kernel.org, wsa+renesas@sang-engineering.com,
        andriy.shevchenko@linux.intel.com, conghui.chen@intel.com,
        arnd@arndb.de, kblaiech@mellanox.com,
        jarkko.nikula@linux.intel.com, Sergey.Semin@baikalelectronics.ru,
        rppt@kernel.org, loic.poulain@linaro.org, tali.perry1@gmail.com,
        u.kleine-koenig@pengutronix.de, bjorn.andersson@linaro.org,
        yu1.wang@intel.com, shuo.a.liu@intel.com, viresh.kumar@linaro.org,
        stefanha@redhat.com, pbonzini@redhat.com
References: <9a2086f37c0a62069b67c39a3f75941b78a0039c.1614749417.git.jie.deng@intel.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <43b0842b-8b0f-1979-ed07-d6124e3a6b79@redhat.com>
Date:   Thu, 4 Mar 2021 17:15:44 +0800
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On 2021/3/4 9:59 上午, 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.
>
> 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>
> ---
>   drivers/i2c/busses/Kconfig      |  11 ++
>   drivers/i2c/busses/Makefile     |   3 +
>   drivers/i2c/busses/i2c-virtio.c | 289 ++++++++++++++++++++++++++++++++++++++++
>   include/uapi/linux/virtio_i2c.h |  42 ++++++
>   include/uapi/linux/virtio_ids.h |   1 +
>   5 files changed, 346 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..0860395 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


Please use select here. There's no prompt for 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..b88da08 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..98c0fcc
> --- /dev/null
> +++ b/drivers/i2c/busses/i2c-virtio.c
> @@ -0,0 +1,289 @@
> +// 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/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 - 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;
> +};
> +
> +/**
> + * 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;
> +	u8 *buf;
> +	struct virtio_i2c_in_hdr in_hdr;
> +};
> +
> +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;
> +	u8 *buf;
> +
> +	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 |= 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;
> +
> +		buf = kzalloc(msgs[i].len, GFP_KERNEL);
> +		if (!buf)
> +			break;
> +
> +		reqs[i].buf = buf;
> +		sg_init_one(&msg_buf, reqs[i].buf, msgs[i].len);
> +
> +		if (msgs[i].flags & I2C_M_RD) {
> +			sgs[outcnt + incnt++] = &msg_buf;
> +		} else {
> +			memcpy(reqs[i].buf, msgs[i].buf, msgs[i].len);
> +			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);
> +			kfree(reqs[i].buf);
> +			reqs[i].buf = NULL;
> +			break;
> +		}
> +	}
> +
> +	return i;
> +}
> +
> +static int virtio_i2c_complete_reqs(struct virtqueue *vq,
> +					struct virtio_i2c_req *reqs,
> +					struct i2c_msg *msgs, int nr)
> +{
> +	struct virtio_i2c_req *req;
> +	unsigned int len;
> +	int i;
> +
> +	for (i = 0; i < nr; i++) {
> +		req = (struct virtio_i2c_req *)virtqueue_get_buf(vq, &len);


The case is unnecessary.


> +		if (!(req && req == &reqs[i])) {
> +			pr_err("msg[%d]: addr=0x%x virtqueue error.\n", i, msgs[i].addr);
> +			break;
> +		}


It's better to be more specific here, e.g we can say we saw out of order 
completion here.


> +
> +		if (req->in_hdr.status != VIRTIO_I2C_MSG_OK) {
> +			pr_err("msg[%d]: addr=0x%x backend error.\n", i, msgs[i].addr);
> +			break;


Don't we need to clean used ring by keeping calling virtqueue_get_buf() 
here?


> +		}
> +
> +		if (msgs[i].flags & I2C_M_RD)
> +			memcpy(msgs[i].buf, req->buf, msgs[i].len);


Sorry if I had asked this before but any rason not to use msg[i].buf 
directly?


> +
> +		kfree(req->buf);
> +		req->buf = NULL;
> +	}
> +
> +	return i;
> +}
> +
> +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->i2c_lock);
> +
> +	ret = virtio_i2c_send_reqs(vq, reqs, msgs, num);
> +	if (ret == 0)
> +		goto err_unlock_free;
> +
> +	nr = ret;
> +
> +	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 = -ETIMEDOUT;
> +		goto err_unlock_free;


So if the request is finished after the timerout, all the following 
request will fail, is this expected?


> +	}
> +
> +	ret = virtio_i2c_complete_reqs(vq, reqs, msgs, nr);


So consider driver queue N requests, can device raise interrupt if it 
completes the first request? If yes, the code break, if not it need to 
be clarified in the spec.

Acaultly I remember there's no VIRTIO_I2C_FLAGS_FAIL_NEXT in previous 
versions, and after reading the spec I still don't get the motivation 
for that (it may complicates both driver and device actually).


> +
> +	reinit_completion(&vi->completion);


So if a request it timeout but interrupt is raised here, everything is 
broken.

Thanks


> +
> +err_unlock_free:
> +	mutex_unlock(&vi->i2c_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 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 controlled 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..00f4508
> --- /dev/null
> +++ b/include/uapi/linux/virtio_i2c.h
> @@ -0,0 +1,42 @@
> +/* 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/virtio_ids.h>
> +#include <linux/virtio_config.h>
> +
> +/**
> + * 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;
> +};
> +
> +/* 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_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..6ae32db 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_ADPTER		34 /* virtio i2c adpter */
>   
>   #endif /* _LINUX_VIRTIO_IDS_H */