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

[Jie Deng]

On 2021/2/25 15:21, Viresh Kumar wrote:
> On 12-10-20, 09:55, 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.
> >
> > 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.