Date:   Sat, 4 Sep 2021 16:01:51 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jie Deng <jie.deng@...el.com>
Cc:     linux-i2c@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, wsa@...nel.org,
        wsa+renesas@...g-engineering.com, arnd@...db.de,
        jasowang@...hat.com, andriy.shevchenko@...ux.intel.com,
        yu1.wang@...el.com, shuo.a.liu@...el.com, conghui.chen@...el.com,
        viresh.kumar@...aro.org, stefanha@...hat.com,
        gregkh@...uxfoundation.org
Subject: Re: [PATCH v14] i2c: virtio: add a virtio i2c frontend driver

On Fri, Jul 09, 2021 at 10:25:30AM +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.
> 
> 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@...el.com>
> Signed-off-by: Conghui Chen <conghui.chen@...el.com>
> Signed-off-by: Jie Deng <jie.deng@...el.com>

Same as with qemu bits, I am confused as to what is the status
of proposed spec changes and whether the driver will work
with them. Let's let the dust settle on them then, then
resubmit?

> ---
> Changes v13 -> v14
> 	- Put the headers in virtio_i2c.h in alphabetical order.
> 	- Dropped I2C_FUNC_SMBUS_QUICK support.
> 	- Dropped few unnecessary variables and checks.
> 	- Use "num" everywhere instead of num or nr, to be consistent.
> 	- Added few comments which make the design more clear. 
>  
> Changes v12 -> v13
> 	- Use _BITUL() instead of BIT().
> 	- Rename "virtio_i2c_send_reqs" to "virtio_i2c_prepare_reqs".
> 	- Optimize the return value of "virtio_i2c_complete_reqs".
> 
> Changes v11 -> v12
> 	- Do not sent msg_buf for zero-length request.
> 	- Send requests to host only if all the number of transfers requested prepared successfully.
> 	- Remove the line #include <linux/bits.h> in virtio_i2c.h.
> 
> 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 | 285 ++++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/virtio_i2c.h |  41 ++++++
>  include/uapi/linux/virtio_ids.h |   1 +
>  5 files changed, 341 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..0139cdc
> --- /dev/null
> +++ b/drivers/i2c/busses/i2c-virtio.c
> @@ -0,0 +1,285 @@
> +// 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_prepare_reqs(struct virtqueue *vq,
> +				   struct virtio_i2c_req *reqs,
> +				   struct i2c_msg *msgs, int num)
> +{
> +	struct scatterlist *sgs[3], out_hdr, msg_buf, in_hdr;
> +	int i;
> +
> +	for (i = 0; i < num; i++) {
> +		int outcnt = 0, incnt = 0;
> +
> +		/*
> +		 * We don't support 0 length messages and so masked out
> +		 * I2C_FUNC_SMBUS_QUICK in virtio_i2c_func().
> +		 */
> +		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 != num - 1)
> +			reqs[i].out_hdr.flags = cpu_to_le32(VIRTIO_I2C_FLAGS_FAIL_NEXT);
> +
> +		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;
> +
> +		if (virtqueue_add_sgs(vq, sgs, outcnt, incnt, &reqs[i], GFP_KERNEL)) {
> +			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 num,
> +				    bool timedout)
> +{
> +	struct virtio_i2c_req *req;
> +	bool failed = timedout;
> +	unsigned int len;
> +	int i, j = 0;
> +
> +	for (i = 0; i < num; i++) {
> +		/* Detach the ith request from the vq */
> +		req = virtqueue_get_buf(vq, &len);
> +
> +		/*
> +		 * Condition req == &reqs[i] should always meet since we have
> +		 * total num requests in the vq. reqs[i] can never be NULL here.
> +		 */
> +		if (!failed && (WARN_ON(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 timedout ? -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 count;
> +
> +	reqs = kcalloc(num, sizeof(*reqs), GFP_KERNEL);
> +	if (!reqs)
> +		return -ENOMEM;
> +
> +	count = virtio_i2c_prepare_reqs(vq, reqs, msgs, num);
> +	if (!count)
> +		goto err_free;
> +
> +	/*
> +	 * For the case where count < num, i.e. we weren't able to queue all the
> +	 * msgs, ideally we should abort right away and return early, but some
> +	 * of the messages are already sent to the remote I2C controller and the
> +	 * virtqueue will be left in undefined state in that case. We kick the
> +	 * remote here to clear the virtqueue, so we can try another set of
> +	 * messages later on.
> +	 */
> +
> +	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");
> +
> +	count = virtio_i2c_complete_reqs(vq, reqs, msgs, count, !time_left);
> +
> +err_free:
> +	kfree(reqs);
> +	return count;
> +}
> +
> +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 & ~I2C_FUNC_SMBUS_QUICK);
> +}
> +
> +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@...el.com>");
> +MODULE_AUTHOR("Conghui Chen <conghui.chen@...el.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..7c6a6fc
> --- /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/const.h>
> +#include <linux/types.h>
> +
> +/* The bit 0 of the @virtio_i2c_out_hdr.@...gs, used to group the requests */
> +#define VIRTIO_I2C_FLAGS_FAIL_NEXT	_BITUL(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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