Re: [PATCH v4] i2c: virtio: add a virtio i2c frontend driver

On 2021/2/25 15:21, Viresh Kumar wrote:

On 12-10-20, 09:55, Jie Deng wrote:

quoted

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.

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;
+};

Hi Jie,

I am a bit confused about the header and the format in which data is being
processed here. When I look at the specification present here:

https://lists.oasis-open.org/archives/virtio-comment/202009/msg00021.html

it talks about

struct virtio_i2c_out_hdr {
         le16 addr;
         le16 padding;
         le32 flags;
};
struct virtio_i2c_in_hdr {
         u8 status;
};

struct virtio_i2c_req {
         struct virtio_i2c_out_hdr out_hdr;
         u8 write_buf [];
         u8 read_buf [];
         struct virtio_i2c_in_hdr in_hdr;
};

while what we have above is completely different. What am I missing ?

This v4 was the old version before the specification was acked by the virtio tc.

Following is the latest specification.

https://raw.githubusercontent.com/oasis-tcs/virtio-spec/master/virtio-i2c.tex

I will send the v5 since the host/guest ABI changes.

Thanks.

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