Re: [PATCH v6] i2c: virtio: add a virtio i2c frontend driver

On 2021/3/4 14:06, Viresh Kumar wrote:

Please always supply version history, it makes it difficult to review otherwise.

I will add the history.

quoted

  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

depends on I2C as well ?

No need that. The dependency of I2C is included in the Kconfig in its 
parent directory.

quoted

+	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
+

Not that it is important but I would have added it towards the end instead of at
the top of the file..

I'm OK to add it to the end.

quoted

  # 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>

I don't think above two are required here..

quoted

+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>

same here.

quoted

+#include <linux/wait.h>

same here.

Will confirm and remove them if they are not required. Thank you.

quoted

+

And this blank line as well, since all are standard linux headers.

quoted

+#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;

i2c_ is redundant here. "lock" sounds good enough.

OK.

quoted

+	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.
+		 */

Please use proper comment style.

will fix it.

                 /*
                  * Only 7-bit mode supported for now, check Virtio I2C
                  * specification for format of "addr" field.
                  */

quoted

+		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;

Since flags field hasn't been touched anywhere, directly assigning it may be
better instead of |=, it makes it more readable.

OK.

quoted

+
+		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);

No need of cast here since return type is void *.

Right. Thank you.

quoted

+		if (!(req && req == &reqs[i])) {

I find this less readable compared to:
		if (!req || req != &reqs[i]) {

Different people may have different tastes.

Please check Andy's comment in this link.

https://lists.linuxfoundation.org/pipermail/virtualization/2020-September/049933.html

quoted

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

For all the above errors where you simply break out, you still need to free the
memory for buf, right ?

Will try to use reqs[i].buf = msgs[i].buf to avoid allocation.

quoted

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

I have never worked with i2c stuff earlier, but I don't think you need a lock
here. The transactions seem to be serialized by the i2c-core by itself (look at
i2c_transfer() in i2c-core-base.c), though there is another exported version
__i2c_transfer() but the comment over it says the callers must take adapter lock
before calling it.

Lock is needed since no "lock_ops" is registered in this i2c_adapter.

quoted

+
+	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;

You need to free bufs of the requests here as well..

quoted

+		goto err_unlock_free;
+	}
+
+	ret = virtio_i2c_complete_reqs(vq, reqs, msgs, nr);
+
+	reinit_completion(&vi->completion);
+
+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,

Why are we using something that is deprecated here ?

Warn users that the adapter doesn't support classes anymore.

quoted

+	.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;

better add a blank line here.

OK.

quoted

+	/* 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");

You can add module-author as well here.

Sure. I'm glad to do that.

quoted

+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>

Any file (header or c) should only include what it directly needs and nothing
else. And so you should need only types.h here and nothing else.

OK.

quoted

+
+/**
+ * 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;
+};

It might be worth setting __packed for the structures here, even when we have
taken care of padding ourselves, for both the structures..

Please check Michael's comment https://lkml.org/lkml/2020/9/3/339.
I agreed to remove "__packed" .

quoted

+
+/* The bit 0 of the @virtio_i2c_out_hdr.@flags, used to group the requests */
+#define VIRTIO_I2C_FLAGS_FAIL_NEXT	0x00000001
+

I would define this before the above structure.

OK.

quoted

+/**
+ * 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 */

Thanks for yet another version Jie.

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