linux-kernel - Re: [PATCH v5] i2c: virtio: add a virtio i2c frontend driver

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Message-ID: <5e66fc1b-81d3-341e-4864-adb021e9ce1e@intel.com>
Date:   Tue, 2 Mar 2021 13:06:49 +0800
From:   Jie Deng <jie.deng@...el.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Linux I2C <linux-i2c@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Wolfram Sang <wsa@...nel.org>,
        Jason Wang <jasowang@...hat.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        conghui.chen@...el.com, kblaiech@...lanox.com,
        jarkko.nikula@...ux.intel.com,
        Sergey Semin <Sergey.Semin@...kalelectronics.ru>,
        Mike Rapoport <rppt@...nel.org>, loic.poulain@...aro.org,
        Tali Perry <tali.perry1@...il.com>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        yu1.wang@...el.com, shuo.a.liu@...el.com,
        Stefan Hajnoczi <stefanha@...hat.com>
Subject: Re: [PATCH v5] i2c: virtio: add a virtio i2c frontend driver


On 2021/3/2 12:22, Viresh Kumar wrote:
> On 02-03-21, 09:31, Viresh Kumar wrote:
>> On 01-03-21, 16:19, Arnd Bergmann wrote:
>>> On Mon, Mar 1, 2021 at 7:41 AM Jie Deng <jie.deng@...el.com> wrote:
>>>
>>>> --- /dev/null
>>>> +++ b/include/uapi/linux/virtio_i2c.h
>>>> @@ -0,0 +1,56 @@
>>>> +/* 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
>>> Why is this a uapi header? Can't this all be moved into the driver
>>> itself?
>>>
>>>> +/**
>>>> + * struct virtio_i2c_req - the virtio I2C request structure
>>>> + * @out_hdr: the OUT header of the virtio I2C message
>>>> + * @write_buf: contains one I2C segment being written to the device
>>>> + * @read_buf: contains one I2C segment being read from the device
>>>> + * @in_hdr: the IN header of the virtio I2C message
>>>> + */
>>>> +struct virtio_i2c_req {
>>>> +       struct virtio_i2c_out_hdr out_hdr;
>>>> +       u8 *write_buf;
>>>> +       u8 *read_buf;
>>>> +       struct virtio_i2c_in_hdr in_hdr;
>>>> +};
>>> In particular, this structure looks like it is only ever usable between
>>> the transfer functions in the driver itself, it is shared with neither
>>> user space nor the virtio host side.
>> Why is it so ? Won't you expect hypervisors or userspace apps to use
>> these ?
> This comment applies only for the first two structures as the third
> one is never exchanged over virtio.
Yeah. Actually, the backend only needs "struct virtio_i2c_out_hdr out_hdr"
and "struct virtio_i2c_in_hdr in_hdr" for communication. So we only need 
to keep
the first two in uapi and move "struct virtio_i2c_req" into the driver.

But Jason wanted to include "struct virtio_i2c_req" in uapi. He 
explained in this link
https://lists.linuxfoundation.org/pipermail/virtualization/2020-October/050222.html.
Do you agree with that explanation ?